Etch method using a dielectric etch chamber with expanded process window

ABSTRACT

A method for etching a dielectric in a thermally controlled plasma etch chamber with an expanded processing window. The method is adapted to incorporate benefits of a the thermal control and high evacuation capability of the chamber. Etchent gases include hydrocarbons, oxygen and inert gas. Explanation is provided for enablling the use of hexafluoro-1,3-butadiene in a capacitively coupled etch plasma. The method is very useful for creating via, self aligned contacts, dual damascene, and other dielectric etch.

BACKGROUND OF THE DISCLOSURE

1. Field of Invention

The present invention relates generally to a semiconductor waferprocessing apparatus. More specifically, the invention relates to adielectric etch processing chamber having improved thermal andby-product management capabilities, improved control of gaseous speciesresidence time, and an expanded process window including high flow ratesand low operating pressures.

2. Background of the Invention

One challenge facing all forms of semiconductor processing is theindustry wide progression towards decreasing feature sizes resulting inrapidly shrinking critical dimensions. Current design rules have featuresizes of less than about 0.18 microns and feature sizes below about 0.1microns are being developed.

Another challenge facing semiconductor processing is the trend towardssmaller footprint devices. One approach to achieving a smaller devicefootprint is to build the device structure vertically and in somedevices, fabricating portions of the device in the substrate itself.

These challenges generate a need for processing applications capable offabricating high aspect ratio structures and structures with criticaldimensions approaching the sub-0.1 micron range.

In view of these challenges, minimizing particulate contamination duringthe myriad processing sequences used to fabricate an electronic deviceis critical. Chamber components are selected and processes are performedin reduced atmospheres to assist in reducing and managing particles thatmay be present and/or generated in the processing environment. Ofparticular importance is the management of films that form within theprocess chamber during wafer processing.

Films deposited within the processing chamber are major contributors tothe total particulate concentrations found within the process chamber.Films typically form on exposed chamber and process kit componentsduring a wide variety of semiconductor processing applications.

During dielectric etch processes, for example, some of the materialremoved from the layer exposed to the etchant is exhausted from theprocessing chamber. However, some etch reaction by-products formdeposits on exposed chamber surfaces and on surfaces of the etchedstructure.

The deposits on chamber surfaces increase in thickness as the processcycles are repeated and additional wafers are processed. As the depositthickness increases, so too does the internal stresses associated withthe deposit. Additional stresses are created in these deposits due todifferences in thermal expansion rates between the deposit and thechamber surfaces. Conventional etch chambers lack appropriate thermalmanagement techniques to reduce thermally induced stresses betweenaccumulated deposits and chamber components. Eventually, the stressescan cause the deposits to crack, consequently releasing particles intothe chamber environment. These film particles may impinge upon the wafersurface, typically creating a defect in the circuit structure on thewafer.

Control of deposit formation on the etch structure is also a criticalprocess consideration. In high aspect ratio dielectric etch processes,for example, the formation of a thin sidewall layer or passivation layeris desired to help maintain sidewall profile control as the depth of theetched feature increases. As feature sizes decrease, however, sidewallprofile control becomes increasingly more difficult and possiblyunfeasible using conventional plasma etch chambers. Decreasing criticaldimensions require increasingly refined control of an expanded range ofetch process chemistry parameters not provided by conventional etchchambers.

Therefore, there is a need for a dielectric etch processing apparatuswith the capability of providing expanded processing capabilities withimproved process parameter control that enables advanced featuredielectric etch processes.

SUMMARY OF INVENTION

The disadvantages associated with the prior art etch chambers and thechallenges posed by advanced dielectric etch processes are overcome byembodiments of the present invention of a thermally controlled plasmaetch chamber having an expanded process window and improved byproductmanagement capabilities. The inventive procees chamber is generally acapacitively coupled plasma source chamber and, more specifically, acapacitively coupled chamber operating in an RIE mode and MERIE mode.

An embodiment of an apparatus according to the present inventioncomprises a thermally controlled reactor for plasma etch processingsubstrates at subatmospheric pressures, comprising: a vacuum chamberhaving a gas inlet, a gas outlet and an interior surface; a thermallycontrolled liner disposed adjacent to said interior surface saidthermally controlled liner having an internal fluid passageway; athermally controlled substrate support disposed within said vacuumchamber; and temperature of said gas inlet is different said thermallycontrolled liner.

Another embodiment of an apparatus according to the present inventioncomprises a thermally controlled reactor for plasma etch processingsubstrates at subatmospheric pressures, comprising: a vacuum chamberhaving a gas inlet, a gas outlet and an interior surface; a linerdisposed adjacent to said interior; a thermally controlled substratesupport disposed within said vacuum chamber; a vacuum pump system havingcapacity of at least 1600 liter per minute.

Another embodiment of an apparatus according to the present invention isa thermally controlled reactor for plasma etch processing substrates atsubatmospheric pressures, comprising: a vacuum chamber comprising aprocessing volume with a lid, a wall, a gas inlet, a gas outlet disposedwithin said processing volume, said wall having an interior surface; athermally controlled liner disposed adjacent to said interior surfacesaid thermally controlled liner having an internal fluid passageway; anda thermally controlled substrate support disposed within said processingvolume, said thermally controlled substrate support having multipletemperature control zones.

Another embodiment of an apparatus according to the present invention isa thermally controlled plasma processing chamber, comprising: a vacuumchamber comprising a chamber interior; a gas inlet for providing a gasinto said chamber interior; a plasma excitation power source coupled tosaid vacuum chamber so as to excite a portion of the gas within saidchamber interior into a plasma; an exhaust channel coupling said chamberinterior to an exhaust pump and providing a gas flow path between thechamber interior and the exhaust pump; a substrate support disposedwithin said chamber interior; a thermally controlled liner disposedwithin said chamber interior, said thermally controlled liner having anintegrally formed fluid channel; a deflector positioned within theexhaust channel so as to cause turbulence in the gas flow between thechamber interior and the exhaust pump; and a magnet system disposedadjacent to the deflector.

Another embodiment of an apparatus according to the present invention isa thermally controlled plasma processing chamber, comprising: a vacuumchamber comprising a chamber interior; a gas inlet for providing a gasinto said chamber interior; a plasma excitation power source coupled tosaid vacuum chamber so as to excite a portion of the gas within saidchamber interior into a plasma; an exhaust channel coupling said chamberinterior to an exhaust pump and providing a gas flow path between thechamber interior and the exhaust pump, said exhaust channel comprising:an inlet aperture coupled to said chamber interior; an outlet aperturein communication with the vacuum pump; a wall between said inletaperture and said outlet aperture including a protrusion extending intosaid exhaust channel; a substrate support disposed within said chamberinterior; a thermally controlled liner disposed within said chamberinterior, said thermally controlled liner having an integrally formedfluid channel; and a deflector positioned within the exhaust channel soas to cause turbulence in the gas flow between the chamber interior andthe exhaust pump; and a magnet system disposed adjacent to thedeflector.

An embodiment of an etch method according to the present invention is amethod of plasma etching features on an oxide layer on a substratedisposed in a thermally controlled plasma etch chamber, comprising:disposing a substrate in a processing region of a thermally controlledplasma etch chamber; controlling the temperature of a wall disposedadjacent to the processing region of the thermally controlled plasmaetch chamber; controlling the temperature of a substrate support;maintaining a pressure in the processing region; flowing a gascomposition through a thermally differentiated nozzle and into theprocessing region; coupling RF energy into the processing region to forma plasma from the gas composition; and providing a magnetic fieldtransverse to a pumping annulus in communication with the processingregion.

An embodiment of an etch method according to the present invention is amethod of plasma etching features on an oxide layer on a substratedisposed in a magnetically enhanced thermally controlled plasma etchchamber, comprising: disposing a substrate in a processing region of athermally controlled plasma etch chamber; controlling the temperature ofa wall disposed adjacent to the processing region of the thermallycontrolled plasma etch chamber; controlling the temperature of asubstrate support; maintaining a pressure in the processing region;flowing a gas composition through a thermally differentiated nozzle andinto the processing region; coupling RF energy into the processingregion to form a plasma from the gas composition; and providing amagnetic field in the processing region and transverse to the substrate.

Another embodiment of an etch method according to the present inventioncomprises: disposing a substrate in a processing region of a thermallycontrolled plasma etch chamber; controlling the temperature of a walldisposed adjacent to the processing region of the thermally controlledplasma etch chamber; controlling the temperature of a substrate support;maintaining a pressure in the processing region; flowing a gascomposition into the processing region; coupling RF energy into theprocessing region to form a plasma from the gas composition; providing amagnetic field in the processing region and transverse to the substrate;and evacuating the chamber at a rate of at least 1600 liter per minute.

BRIEF DESCRIPTION OF DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a cross-sectional schematic view of a parallel platesemiconductor wafer processing system;

FIG. 2 is a cross-sectional schematic view of a semiconductor waferprocessing system illustrating an embodiment of an upper and a lowerliner according to the present invention;

FIG. 3A is a plan view of a lid assembly having the first liner of FIG.2;

FIG. 3B is a plan view of another lid assembly;

FIG. 4 is a partially exploded elevation of the lid assembly of eitherFIG. 3A or 3B;

FIG. 5 is plan view of the second liner of FIG. 2;

FIG. 6 is a cross-sectional view of the second liner of FIG. 5 takenalong section line 5—5;

FIGS. 7a-7 f are various embodiments of a gas inlet;

FIG. 8 is a plan view of the ceiling interior surface corresponding toFIG. 2.

FIG. 9 is a plan view of an individual mini-gas distribution plate ofthe invention having angled gas inlets providing a preferred vortexpattern of gas spray.

FIG. 10 is a cross-sectional cut-away view corresponding to FIG. 9.

FIG. 11 illustrates an alternative spray pattern corresponding to FIG.4.

FIG. 12 is an enlarged cut-away cross-sectional view corresponding toFIG. 2.

FIGS. 13 and 14 are top and sectional views, respectively, of a plate inwhich has been formed a texture consisting of square protrusions.

FIG. 15 is a sectional view of an alternative to the embodiment of FIG.14 in which the sides of the square depressions are formed at an obliqueangle.

FIGS. 16 and 17 are top and sectional views, respectively, of analternative embodiment in which the depressions are hemispherical inshape.

FIGS. 18 and 19 are perspective and sectional views, respectively, of atexture consisting of a series of circumferential grooves in acylindrical side wall liner.

FIG. 20 is a perspective view of a cylindrical liner having bothcircumferential and longitudinal grooves.

FIG. 21 is a plan view of a plasma etching chamber with an exhaustmanifold having an annular, U-shaped magnet system embedded within anannular protrusion according to the invention.

FIG. 22 is a detail of the magnet system and annular protrusions in theFIG. 21 chamber.

FIG. 23 is a perspective view of an annular, U-shaped magnet system withmagnetic poles facing radially outward.

FIG. 24 is a perspective view of a magnet system whose magnets and polepieces are interchanged relative to the embodiment of FIG. 23.

FIG. 25 is a perspective view of an annular, U-shaped magnet system withmagnetic poles facing radially inward.

FIG. 26 is a perspective view of a magnet system whose magnets and polepieces are interchanged relative to the embodiment of FIG. 25.

FIG. 27 is a detailed plan view of an exhaust manifold having twoannular magnets respectively embedded within two annular protrusionsaccording to the invention.

FIG. 28 is a cross-section partial schematic view of an alternativeembodiment of the present invention in a capacitively coupled,magnetically enhanced reactive ion etch (MERIE) processing system;

FIG. 29 is a cross-section partial schematic view of an alternativeembodiment of the present invention in a parallel plate etch processingsystem;

FIG. 30 is a cross-section partial schematic view of an alternativeembodiment of the present invention in a, capacitively coupled,magnetically enhanced reactive ion etch (MERIE) processing systemgenerated by a rotating magnetic field;

FIG. 31 is a cross-section partial schematic view of an alternativeembodiment of the present invention in an etch processing system havingan RF driven inductive member;

FIG. 32 is a cross-sectional schematic view of another semiconductorwafer processing system having a chamber liner with a showerhead gasdistribution system and an inductive coil;

FIGS. 33A and 33B are cross-section views of a representativeself-aligned contact feature;

FIGS. 34A and 34B are cross-section views of a representative highaspect ratio contact feature;

FIGS. 35A and 35B are cross-section views of a representative viafeature;

FIGS. 36A and 36B are cross-section views of a representative mask openfeature;

FIGS. 37A and 37B are cross-section views of a representative spacerfeature; and

FIGS. 38A and 38B are cross-section views of a representative dualdamascene feature.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION OF THE INVENTION

I. Exemplary Processing System

FIG. 1 illustrates an embodiment of the processing apparatusimprovements of the present invention in an exemplary processing chamber100 for processing a substrate 10, such as a semiconductor wafer. Theinvention will be described below initially with reference toembodiments as used in the exemplary processing system 50 of FIG. 1.However, it should be understood that the description of the inventivefeatures applies to the alternative chamber configurations such as theetch chamber configurations 2800 to 3200 described below with referenceto FIGS. 28 to 32. Embodiments of the present invention are particularlyadvantageous in plasma etch chambers configured for oxide and dielectricetch processes.

An embodiment of the present invention is illustrated in processingsystem 50 of FIG. 1. Processing system 50 comprises a processing chamber100, a gas panel 105, a computer controller 140, a heat exchanger ortemperature controlled fluid source 121, an RF source 150, a pump 109,an exhaust system 110 and a cooling gas system 107.

The processing chamber 100 includes a circumferential sidewall 106, abottom wall 108 and a lid assembly 102 that together define a chambervolume 110. A substrate support 124 is disposed on bottom wall 108 forsupporting the substrate 10. Generally, the chamber volume 110 isdivided into a process volume 112—the upper region of the chamber—and apumping volume 114—the lower region of the chamber. Chamber liner 104,illustrated as a first liner 134 and a second liner 118, is disposedadjacent to walls 106,108 and lid 102. In an embodiment described ingreater detail below, chamber liner 104 includes a plasma confinementmeans 52 for confining a plasma within process volume 112.

The processing chamber 100 is provided with a slit valve 139 or accessport for transferring substrates from a common loadlock or transfer areainto the processing region 112. A robot 53 (shown in phantom in FIG. 1)is used to transfer substrates in and out of processing region 112. Aslit valve door (not shown) provides a vacuum seal of the slit valveopening 139. A liner door 70 could be a vertically actuated via apneumatic motor 72 as illustrated in FIG. 1 to cover the opening in thechamber liner 104 adjacent the slit valve opening 139.

Substrate support 124 may use electrostatic force or mechanical clampingforce to ensure the substrate 10 remains in place during processing. Ifelectrostatic force is used, substrate support 124 includeselectrostatic chuck 55. A lift pin assembly 155 comprises lift pins 160a,b that are elevated through holes in the electrostatic chuck 55 by apneumatic lift mechanism 170. The robot 53 places the substrate 10 onthe lift pins 160 a,b, and the pneumatic lift mechanism 170 lowers thesubstrate 10 onto the receiving surface of electrostatic chuck 55. Afterthe substrate 10 is placed on the electrostatic chuck 55 and prior toconducting a process, an electrode 105 embedded in the electrostaticchuck 55 is electrically biased with respect to the substrate 10 toelectrostatically hold the substrate 10.

On completion of the process, the pneumatic lift mechanism 170 raisesthe lift pins 160 to raise the substrate 10 off the receiving surface ofelectrostatic chuck 55, allowing the substrate 10 to be removed by therobot 53. Before raising the lift pins 160 a,b, the substrate 10 iselectrically decoupled or de-chucked by dissipating the residualelectrical charges holding the substrate 10 to the electrostatic chuck55.

In the embodiment illustrated in FIG. 1, electrostatic chuck 55 isformed from a dielectric that envelops and electrically isolates theelectrode 105 from the substrate 10. Preferably, the dielectric is aceramic material, such as Al₂O₃, AlN, BN, Si, SiO₂, Si₃N₄, TiO₂, ZrO₂,codierite, mullite, or mixtures and compounds thereof In one embodiment,the electrostatic chuck 55 is formed from a high thermal conductivityceramic material with a resistivity selected for optimal performance inthe temperature range that the substrate 10 is maintained. For example,resistivity in the range of between about 5 e¹⁰ Ω-cm to about 5 e¹³Ω-cm, for example, have been used where substrate temperatures in therange of between about −20° C. to about 50° C. are desired.

An electrode 105 disposed within substrate support 124 couples RF energyinto process volume 112. RF energy from RF source 150 is coupled toelectrode 105 via impedance matching circuitry 151. Electrode 105 may beformed from an electrically conducting material, such as a metal, forexample, aluminum, copper, molybdenum or mixtures thereof Generally,electrode 105 has a robust construction that allows coupling of up toabout 5000 Watts of RF power from RF generator 150. The exact amount ofRF power coupled through robust electrode 105 varies depending upon theparticular etch process conducted within etch chamber 100.

A backing plate 161 is disposed adjacent to electrostatic chuck 55. Thebacking plate 161 has internal cooling channels supplied withtemperature controlled fluid from heat exchanger 121 via inlet 163. Thetemperature controlled fluid, such as for example, an ethylene glycoland de-ionized water mixture, circulates through the conduits in thecooling plate. Preferably the electrostatic chuck 55 is attached to thebacking plate 161 so as to maximize heat transfer from the electrostaticchuck 55 to the backing plate cooling channels and thence to thetemperature controlled fluid.

In another aspect of the present invention, the backing plate 161 isbonded or joined to the electrostatic chuck 55 by a bond layer made froma material having high thermal conductivity. The bond layer cancomprise, for example a metal, such as aluminum, copper, iron,molybdenum, titanium, tungsten or alloys thereof, such as for example,titanium diborite. The bond layer eliminates use of bolts for securingthe electrostatic chuck 55 to the cooling plate 161 and consequentlyreduces mechanical stresses on the electrostatic chuck 55. Also, thebond layer has a homogeneous composition that provides more uniform heattransfer rates across the substrate 10, and reduces the differences inthermal impedances that occur at the interface between the cooling plate161 and the electrostatic chuck 55.

Preferably, the bond layer is ductile and compliant to provide aninterface that absorbs the thermal stresses arising from the thermalexpansion mismatch between the electrostatic chuck 55 and the coolingplate 161 without damaging the electrostatic chuck 55. While a bondedjoint provides uniform heat transfer rates, it is often difficult for abonded joint to withstand the thermal stresses arising from differencesin thermal expansion coefficients of dissimilar materials, such as theelectrostatic chuck 55 and the cooling plate 161. An exemplary bondlayer is made from a ductile and compliant material that can flex andabsorb thermal stresses that arise from the difference in thermalexpansion coefficients of the electrostatic chuck 55 and the coolingplate 161. One suitable bonding material consists of a high bondstrength, pressure sensitive acrylic adhesive, loaded with titaniumdiboride and applied to an expanded aluminum carrier. The combination offiller, expanded metal and embossed surface enhances the conformabilityand thermal performance of the bond.

The temperature of the substrate 10 is controlled by stabilizing thetemperature of the electrostatic chuck 55 and providing a cooling gas,such as helium, from cooling gas source 107 to channels formed by theback of the substrate 10 and grooves formed on the receiving surface ofelectrostatic chuck 55. The cooling gas facilitates heat transferbetween the substrate 10 and the electrostatic chuck 55. The spacebetween the backside of the wafer 10 and the receiving surface of theelectrostatic chuck 55 is preferably divided into two zones—an innerzone and an outer zone. Separate flow controllers 107 _(o) and 107 _(i)are used to provide independent cooling gas flow control to the outerand inner zones, respectively. Typically, the desired amount of coolinggas is measured in pressure, generally, in Torr.

Separate zone controllers 107 _(i) and 107 _(o) allow the zones to bemaintained at the same pressure or at different pressures. Adjusting thepressure in the inner and outer zones leads to a correspondingadjustment in the temperature at the center and edge of the substrate10. Thus, by adjusting the pressure of the inner and outer zones thetemperature profile across the substrate 10 is controlled. Thetemperature across the substrate 10 may be adjusted to compensate forthe specific temperature requirements of a particular etch process. Forexample, the temperature across the substrate may be uniform from centerto edge, have a higher edge temperature than center temperature or havea higher center temperature than edge temperature.

During plasma processes, the substrate 10 is heated by plasma in thechamber and the dual zone cooling gas control is used to adjust thesubstrate temperature. Typically, substrate 10 is maintained in atemperature range of between about −20 to about 150 degrees Celsius witha preferred operating range of about 15 to about 20 degrees Celsius. Theinner and outer cooling gas zones can also be operated to induce athermal gradient across substrate 10. For example, the inner zone andthe outer zone cooling gas pressures can be adjusted so that thetemperature in the center of the substrate 10 is greater than or lessthan the temperature at the edge of the substrate 10. In addition, theinner and outer cooling gas zones may be adjusted so that thetemperature difference across the center to edge of the substrate 10 isabout 5 C. or where the temperature between the center and edge remainsnearly constant.

The components of substrate support 124 including cooling plate 161, anelectrostatic chuck 55, dual zone backside cooling gas and robustelectrode 105 cooperatively operate to remove heat generated duringplasma processing operations conducted in chamber 100. The thermalmanagement and temperature control features enable processing operationsthat employ higher RF powers and higher magnetic fields (for chambersusing magnetically enhanced processing) for longer process times becausethe temperature of substrate 10 can be efficiently controlled evenduring processes combining both RF power levels above 2500 W andmagnetic fields greater than 100 G. The temperature control and thermalmanagement capabilities of etch chamber 100 are furthered by the directtemperature control feature of liners 118 and 134 described below insection II entitled “Temperature Controlled Chamber Liner.”

Gas panel 105 includes process gas supplies and flow control valveswhich under the control of computer controller 140 provide process gasesto process chamber 100. Process gases from gas panel 105 are providedvia piping 103 through lid assembly 102 to a plurality of gas inlets ornozzles 350. A plurality of nozzles 350 are distributed across the lidassembly 102 for providing process gases into processing volume 112 asdescribed in greater detail below in section III entitled “Thermallydifferentiated Gas Supply System”.

In operation, a semiconductor substrate 10 is placed on the substratesupport 124 and gaseous components are supplied from the gas panel 105to the process chamber 100 through nozzles 350 to form a desired gascomposition in the processing volume 112. The gas composition is ignitedinto a plasma in the process chamber 100 by applying RF power from theRF generator 150 to impedance matching circuitry 151 to the electrode105. The plasma formed from the gas composition is in contact with thetemperature controlled surfaces of the lid assembly 102 and the liner104.

The pressure within the process chamber 100 is controlled using athrottle valve 8 situated between the chamber volume 110 and a vacuumpump 109. In a preferred embodiment, the pump 109 provides a pumpingcapacity of greater than about 1000 liters per second, preferablybetween about 1,400 to 2,000 liters per second, and more preferablyabout 1,600 liter per second. Pump 109 may be a single high capacityvacuum pump or a combination of a vacuum pump and a turbo pump. Underthe control of controller 140, the pump 109 and the throttle valve 8cooperatively operate to provide an advantageously expanded pressure andgas flow rate plasma etch processing regime. In a preferred embodiment,the plasma etch chamber is a thermally controlled etch chamber capableof performing both magnetically enhanced reactive ion etching (MERIE)and reactive ion etching (RIE) etch processes in a low pressure—hightotal gas flow regime, such as for example, a total gas flow of morethan about 350 sccm and a chamber pressure of less than about 80 mT.Preferably, an embodiment of a process chamber according to the presentinvention enables chamber pressures below about 50 mT with total flowrates of about 1000 sccm.

Plasma etch chambers having embodiments of the present invention arecapable of low pressure—low flow dielectric etch processes such as forexample, spacer etching and mask open etching generally conducted atpressures of between about 10 mT to about 80 mT with total gas flowrates of from about 40 sccm to about 150 sccm. Plasma etch chambershaving embodiments of the present invention are also capable ofhigh-pressure high flow rate dielectric etch processes such as, forexample, C₄F₈ and C₂F₆ based etch processes conducted at pressures ofbetween about 150 mT to about 300 mT and total gas flow rates of betweenabout 350 sccm to about 700 sccm. Plasma etch chambers havingembodiments of the present invention are also capable of high total gasflow—low chamber pressure etch processes such as, for example, C₄F₆ andCH₂F₃ based etching of self aligned and high aspect ratio contacts atpressures of from between about 10 mT to about 120 mT and total gas flowrates of between about 600 sccm to about 900 sccm.

Additionally, plasma etch chambers having embodiments of the presentinvention enable etch processes in a variety of processing regimes, suchas for example, an etch process regime with a total gas flow rangingfrom about 120 sccm to about 400 sccm at a chamber pressure ranging fromabout 70 mT to about 120 mT; an etch processing regime with a total gasflow ranging from about 100 sccm to about 450 sccm at chamber pressuresranging from about 20 mT to about 70 mT; and an etch processing regimehaving total gas flows ranging from about 300 sccm to about 800 sccm atchamber pressures ranging from about 20 mT to about 70 mT. Section VIIbelow entitled “Chamber Process Window And Representative CriticalDielectric Etch Processes” provides additional details of the improvedoxide and dielectric etch process window enabled by plasma etch chambershaving embodiments of the present invention.

A controller 140 comprising a central processing unit (CPU) 144, amemory 142, and support circuits 146 for the CPU 144 is coupled to thevarious components of the process chamber 100 to facilitate control ofthe chamber. To facilitate control of the chamber as described above,the CPU 144 may be one of any form of general purpose computerprocessors that can be used in an industrial setting for controlling thevarious chamber components and even other processors in a processingsystem where computer controlled chamber components are utilized. Thememory 142 is coupled to the CPU 144. The memory 142, or computerreadable medium, may be one or more of readily available memory such asrandom access memory (RAM), read only memory (ROM), floppy disk drive,hard disk, or any other form of digital storage, local or remote. Thesupport circuits 146 are coupled to the CPU 144 for supporting theprocessor in a conventional manner. Support circuits 146 include cache,power supplies, clock circuits, input/output circuitry and subsystems,and the like. A process, such as the etch process, is generally storedin the memory 142, typically as a software routine. The software routinemay also be stored and/or executed by a second CPU (not shown) that isremotely located from the hardware being controlled by the CPU 144.

The software routine executes a process, such as an etch process, tooperate the chamber 100 to perform the steps of the process. Whenexecuted by the CPU 144, the software routine transforms the generalpurpose computer into a specific process computer (controller) 140 thatcontrols the chamber operation to perform the steps of the process.Although embodiments of the present invention are discussed as beingimplemented as a software routine, some or all of the method steps thatare discussed herein may be performed in hardware as well as by thesoftware controller. As such, the invention may be implemented insoftware and executed by a computer system, in hardware as anapplication-specific integrated circuit or other type of hardwareimplementation, or in a combination of software and hardware.

II. Temperature Controlled Chamber Liner

Temperature controlled chamber components, such as a chamber liner 104and lid assembly 102, for use in an etch processing system such asprocessing system 50 may be better appreciated by reference to FIGS.2-6. Embodiments of the present invention also provide methods forcontrolling the temperature of chamber components, to substantiallyimprove adhesion of deposits formed on these chamber components.

FIG. 2 is a cross sectional view of one embodiment of an etch chamber100 of the present invention having a chamber liner 104. The etchchamber 100 is configured as a parallel plate etch reactor. Generally,the chamber liner 104 comprises a first (first) liner 134, a second(second) liner 118, or both a first liner 134 and a second liner 118.Disposed within each chamber liner 104 is at least one passage formed atleast partially therein having an inlet and outlet adapted to flow afluid through the passage from a temperature controlled, fluid supplysystem, such as heat exchanger 121. To facilitate description of theliner of the present invention, an embodiment of the liner of thepresent invention will be described as having a first 134 and a second118 liner. One of ordinary skill will appreciate that a single piece,removable liner may be fabricated and used in lieu of upper 134 andlower 118 liners. It is also to be appreciated that different sizedupper 134 and lower 118 liners may be utilized and that the embodimentsillustrated herein are used merely as an aid in describing the presentinvention. The upper liner 134 and lower liner 118 will now be discussedin turn.

The chamber 100 generally includes an annular sidewall 106, a bottomwall 108, and a lid assembly 102 that define a chamber volume 110.Generally, the chamber volume 110 is bifurcated into a process volume112 (the upper region of the chamber) and a pumping volume 114 (thelower region of the chamber).

The bottom wall 108 has a pumping port 138 through which excess processgases and volatile compounds produced during processing are exhaustedfrom the chamber 100 to exhaust system 110 by a vacuum pump 109. Thebottom wall 108 additionally has two apertures 116 (only one of which isshown in FIG. 2) that provide access to the second liner 118 from theexterior of the chamber 100.

Embodiments of the lid assembly 102 are detailed in the plan views ofFIGS. 3A, 3B and cross-sectional view of FIG. 4. In one embodimentillustrated in FIG. 4, the lid assembly 102 comprises the first liner134 and a lid 202. The first liner 134 has an outwardly extending flange342 that rests upon the top of the sidewall 106. The various componentsof lid assembly 102 are appropriately configured to provide a gas tightseal where needed to ensure the vacuum integrity of the processingvolume 112. For example, lid assembly 102 may be generally biaseddownwardly when the lid 202 is clamped in place, the lid assembly 102exerts a downward force upon the second liner 118 when installed in theprocessing chamber 100.

Continuing with FIG. 4, the first liner 134 is fabricated from athermally conductive material, such as for example, anodized aluminum,stainless steel, ceramic or other compatible material. The first liner134 can be easily removed for cleaning and provides a removable surfaceon which deposition can occur during processing. The first liner 134comprises a center section 310 having a dish-shaped top surface 312, anda bottom surface 316. The dish-shaped top surface 312 has a perimeter314 that is connected to the outwardly extending flange 342. Extendingfrom the bottom surface 316 is a cylindrical liner wall 318. The bottomsurface 316 and liner wall 318 have interior surfaces 320 that areexposed to the process volume 112. As described in greater detail belowin section IV, the interior surfaces 320 of upper liner 134, oroptionally, any liner exposed to process volume 112 may be textured toimprove adhesion of deposited films by reducing surface tension in thefilm.

A fluid passage 322 is disposed within center section 310. The fluidpassage 322 may be formed by a number of conventional means such as, forexample, forming the fluid passage 322 during casting. Turning brieflyto FIG. 3A, another method for forming fluid passage 322 is by drillinga number of intersecting blind holes 208 wherein each hole 208 is sealedby a plug 210, thus forming the fluid passage 322.

Returning to FIG. 4, two bosses 326 (only one of which is shown in FIG.4) protrude from the surface 312 of the center section 310. Each boss326 has a center hole 328 that is fluidly coupled to the fluid passage322 via the respective bore 324.

The fluid passage 322 receives fluid from the heat exchanger or coolantsource 121. Like all surfaces exposed to the plasma, first liner 134 isheated by plasma processes conducted in the plasma etch chamber. Thefluid regulates the temperature of the first liner 134 by drawing heatconducted through the first liner 134 into the fluid. As the fluid iscirculated through the first finer 134 from the fluid source 121, theamount of heat removed form the first liner 134 is controlled, thuspermitting the first liner 134 to be maintained at a predeterminedtemperature.

The fluid, which may be liquid and/or gaseous fluids, is flowed throughthe fluid passage 322 to provide temperature control to the first liner134. The fluid is preferably a liquid such as de-ionized water and/orethylene glycol. Other fluids, such as liquid or gaseous nitrogen orfreon, can also be used. Alternatively, the first liner 134 could beuniformly heated using heated fluids.

One skilled in the art will be able to devise alternate configurationsfor the fluid passage utilizing the teachings disclosed herein. Forexample, as depicted in FIG. 3B, a lid assembly 202 may comprise a firstfluid passage 322A and a second fluid passage 322B. The first and secondfluid passages 322A and B may share a common inlet 330 i and a commonoutlet 330 o as illustrated in FIG. 3B. Optionally, additional inletsand outlets may be utilized. The first and second fluid passages 322Aand 322B double back in a “two tube pass” configuration. Additional tubepasses may alternatively be incorporated.

Returning to FIGS. 3A and 4, quick-connect fluid couplings are utilizedto fluidly connect a fluid supply 121 and the first liner 134 tofacilitate the rapid removal and replacement of the first liner 134 fromthe chamber 100. Typically, a quick-connect 330 having a male pipethread-form is threaded into a female thread-form in the center hole 328of the boss 326. The mating coupling 332 is affixed to the terminal endof a fluid supply line 334. The fluid supply line 334 couples thepassage 322 to the fluid supply 121. One advantage of this configurationis that during the change out of the first liner 134, the fluid supplyline 334 can be disconnected without the aid of tools. However, othermeans of coupling the first liner 134 to the fluid supply line 334 (forexample, pipe threads, barbed nipples, collet connectors and the like)may also be used. Quick-connects are commercially available and aregenerally selected based on port size (thread-form and flow capacity)and the brand used in a particular wafer processing facility or fab (formaintenance inventory purposes).

Returning to FIG. 4, the liner wall 318 is sized to slip inside thesidewall 106 with minimal clearance. The liner wall 318 may vary inheight, and may, when used without a second liner, extend to the chamberbottom 108. Generally, if both the first liner 134 and second liner 118are utilized (as shown in FIG. 2), the liners are proportioned to fitinside the chamber 100 to provide the compressive force necessary toseal the second liner 118 to the chamber bottom 108 when the lidassembly 102 is clamped in place.

The liner wall 318 may additionally contain a number of other ports forvarious purposes. An example of such other ports is a substrate accessport to align with the slit opening of the chamber 100.

Returning to FIG. 2, the second liner 118 will now be described. Thesecond liner 118 is disposed in the chamber 100 to surround thesubstrate support 124 and form a deposition area that can be easilyremoved and cleaned.

The second liner 118 has a fluid passage 119 in which fluid is providedfrom the fluid source 121 by a conduit 123. As with the operation of thefirst liner 134, the fluid regulates the temperature of the second liner118 by drawing heat conducted through the second liner 118 into thefluid. As the fluid is circulated through the second liner 118 from thefluid source 121, the amount of heat removed form the second liner 118is controlled, thus permitting the second liner 118 to be maintained ata predetermined temperature.

FIGS. 5 and 6 depict the second liner 118 in greater detail. The secondliner 118 is fabricated from a thermally conductive material, forexample anodized aluminum, stainless steel, or other compatiblematerial. The second liner 118 comprises a base section 502 connectingan inner wall 504 and an outer wall 506. The interior surfaces 508 ofthe base section 502, inner wall 504 and outer wall 506 are exposed tothe pumping volume 114. As described in greater detail below in sectionIV entitled “Chamber Surface Alterations to Improve Adhesion,” and withregard to the alternative embodiments illustrated in FIG. 8 and FIGS.13-20, the interior surfaces 508 may be textured to increase improveadhesion of deposited films by reducing surface tension in the film.

The base section 502 contains a fluid passage 119. The fluid passage 119may be formed by conventional means such as those described above withregard to the first liner 134. In one embodiment, the fluid passage 119is substantially circular, beginning and ending adjacent to an exhaustport 520 that is disposed through the second liner 118.

Each end of the fluid passage 119 terminates in a boss 510 thatprotrudes from an exterior surface of the base 502. The boss 510interfaces with the bottom wall 108 and ensures the proper orientationof the second liner 118 in the chamber 100 (i.e., all ports align). Tofacilitate the rapid change out of the second liner 118, quick-connectfluid couplings are utilized between the second liner 118 and a conduit123 that fluidly couples the passage 119 to the fluid source 121.

The inner wall 504 is generally cylindrical and is sized to slip overthe substrate support 124 with minimal clearance. The inner wall 504optionally comprises a plasma containment means 516. Plasma confinementmeans 516 may be, for example, a containment magnet 516 disposed withina protrusion 518 formed within inner wall 504 and facing the outer wall506. The protrusion 518 is positioned away from the base on the innerwall 504 so that the plasma containment magnet 516 resides below thesubstrate support 124 when the second liner 118 is installed. The plasmacontainment magnet 516 may be a samarium magnet 516. Alternativeembodiments of the plamsa confinement feature of the present inventionare described in greater detail below in a section entitled PlasmaConfinement. (FIGS. 21 to 27.)

The outer wall 506 is generally cylindrical and is sized to define aminimal gap with the chamber walls 106. The outer wall 506 may vary inheight, particularly if a first liner 134 is also utilized as describedabove. The outer wall 506 additionally contains the exhaust port 520that aligns with the pumping port 138. The exhaust port 520 maypartially encompass a portion of the base wall 108. The exhaust port 520provides fluid access of gases in the pumping volume 114 to the throttlevalve 8 and vacuum pump 109.

The outer wall 506 may optionally include a throttling ridge 522extending into the pumping volume 114. The throttling ridge 522 ispositioned proximate the protrusion 518 on the inner wall 504 to createan annular flow orifice 524 for controlling the flow of gases movingfrom the process volume 112 to the pumping volume 114. The outer wall506 may additionally contain a number of other ports for variouspurposes. An example of such other ports is a substrate access port 526that aligns with a slit opening 139 in the sidewall 106 to allowtransfer of substrate 10 in and out of the chamber 100. Turning brieflyto FIG. 28 which illustrates another embodiment of liner 118, outer wall506 does not include a throttling ridge 522 and only protrusion 518extends into pumping volume 114.

The operation of a temperature controlled liner according to the presentinvention can be illustrated while viewing FIG. 2. In operation, thetemperature of the first liner 134 and second liner 118 are controlledby flowing fluid through the passages 119 and 322 within the respectiveliners 118 and 134, from the fluid source 121. The fluid regulates thetemperature of the liners 118 and 134 by transferring heat between theliners 118 and 134 and the fluid. The fluid from the fluid source 121 iscontrolled in both temperature and rate of flow, thus controlling theamount of heat removed from the liners 118 and 134, and permitting theliners 118 and 134 to be maintained at a predetermined temperature. Inan exemplary embodiment, a user provides a set point for liner walltemperature, for example, into controller 140 and controller 140regulates the amount and temperature of fluid output by heat exchanger121 to maintain the user input setpoint.

Because the temperature of the liners 118 and 134 is controlledpredominantly by the fluid in the passages 119 and 322 and less reliantupon conduction with the chamber walls 106, the liners 118 and 134 areable to maintain a substantially uniform, controllable temperatureduring a variety of plasma etch process conditions, such as for example,increased RF powers and higher magnetic fields. Thus, by controlling thetemperature of the chamber liner 104, the amount of material depositedupon the chamber liner 104 can be better controlled and the stresseswithin the deposited material can be minimized thereby improvingadhesion of the deposited material. Because the temperature controlledliners enables improved adhesion of generated by-products, a widervariety of process gas compositions including deposit formingchemistries such as those encountered in oxide an dielectric etchprocess may be used with greater confidence. Process engineers havegreater latitude in devising etch gas compositions because thebyproducts formed by these gas compositions pose less of a contaminationthreat because of the improved adhesion capability of the liners of thepresent invention. In this way, the process window of etch chambershaving embodiments of the present invention are expanded to include awider variety of useable etch gas compositions.

III. Thermally Differentiated Gas Supply System

Returning to FIG. 4, an embodiment of the gas distribution system of thepresent invention will now be described. The top surface 312 of thefirst liner 134 comprises a center depression 336. The center depression336 is covered by the lid 202, defining a plenum 338 at least partiallybetween the lid 202 and the center depression 336. The lid 202additionally has a central hole 340 that allows fluid flow from apassage 344 in a gas feedthrough 212 fastened to the lid 202. The gasfeedthrough 212 is sealed to the lid 202 to prevent gas leakage. The gasfeedthrough 212 is generally coupled to fluid passages within thesidewall 106 as to allow temperature conditioning of gases beingdelivered to the plenum 338 from the gas source (not shown).Alternatively, the gas feedthrough 212 may be directly coupled to thegag source.

In one embodiment, the plurality of apertures 348 is disposed at leastpartially in the center depression 336. The apertures 348 are generallypositioned in a polar array about the center of the first liner 134,although other positional locations may be utilized. Each aperture 348is fitted with a nozzle 350 a. The nozzles 350 a facilitate distributionof process and other gases from within the plenum 338 to the processvolume 112 of the chamber 100. The nozzle 350 a is generally fabricatedfrom a non-conductive material, such as quartz, silicon carbide,silicon, aluminum nitride, aluminum oxide, Y2O3, Boron Carbide, or othermaterials such as sapphire.

FIGS. 7a-7 f depict various alternative embodiments of the nozzle 350 athat advantageously minimize recirculative gas flows within the chamber.While reference numbers 350 and 350 a are used, it is to be appreciatedthat alternative nozzles 350 b to 350 f may be used. Turning now to FIG.7A. In one embodiment of the nozzle illustrated in FIG. 7A, the nozzle350 a includes a mounting portion 717 and a gas delivery portion 715that is in communication with the chamber volume 110. The mountingportion 717 has a flange 710 extending from the perimeter of the nozzle350 a typically towards the side of the nozzle 350 a exposed to theplenum 338. The nozzle 350 a additionally comprises a central passage724 that fluidly couples the plenum 338 to the chamber volume 110. Thecentral passage 724 generally is positioned co-axially to the centerlineof the nozzle 350 a. Optionally, additional passages may be utilized tofluidly couple the plenum 338 and the chamber volume 110. Additionally,the gas delivery portion of a nozzle may be flush with the first liner134 as illustrated, for example, in nozzle 350 a of FIG. 7A and nozzle350 b of FIG. 7B. Alternatively, the gas delivery portion of a nozzlemay extend beyond the first liner 134 as illustrated, for example, innozzle 350 c of FIG. 7C, in nozzle 350 d of FIG. 7D, in nozzle 350 e ofFIG. 7E, and in nozzle 350 f of FIG. 7F.

Returning to FIG. 7A, the flange 710 mates with a recess 712 disposed inthe first liner 134. Generally, a contact surface 702 of the flange 710and a mating surface 704 of the recess 712 have a surface finish havinga flatness of about 1 mil or less which provides minimal gas leakagebetween the contact surface 702 and the mating surface 704. A exposedsurface 716 of the gas delivery portion 715 may have a smooth ortextured surface.

FIG. 7B illustrates another embodiment of a nozzle, a nozzle 350 b, thatis substantially similar to nozzle 350 a with the exception that centralpassage 724 is optional. The nozzle 350 b has a one or more passages 714that provide fluid communication of the plenum 338 with the chambervolume 110. Generally, the passages 714 are at an angle to thecenterline of the nozzle 350 b. Optionally, the mounting portion 717 mayextend into the plenum 338.

FIG. 7C illustrates another embodiment of a nozzle, a nozzle 35Oc, thatcomprises the mounting portion 717 and the gas delivery portion 735. Thegas delivery portion has an end 728 proximate the mounting portion 717and an opposing, distal end 718 that protrudes into the chamber volume110. The proximate end 728 is generally coplanar or tangent to a surfaceof the first liner 134 exposed to the chamber volume 110. The gasdelivery portion 735 may have a smooth or textured surface finish. Acentral passage 720 extend at least partially through the nozzle 350 cfrom a side 722 of the mounting portion 717 exposed to the plenum 338.One or more secondary passages 726 fluidly couple the central feed 720and the chamber volume 110.

Generally, an outlet 727 of each of the secondary passages 726 on theexterior of the gas delivery portion 735 are positioned at least adistance “DIST” from the end 728 of the gas delivery portion 735.Additionally, the secondary passages 726 are orientated at an angle θrelative to the proximate end 728. In one embodiment, DIST is greaterthan about 0.25 inches and θ ranges between about 15 and about 35degrees.

FIG. 7D illustrates another embodiment of the nozzle, nozzle 350 d, thatis similar to the nozzle 350 c. The nozzle 350 d, however, additionallycomprises a central passage 724 that extends along the centerline of thenozzle 350 c, communicating the plenum 338 directly with the chambervolume 110.

FIG. 7E illustrates another embodiment of a nozzle, a nozzle 350 e, thatis similar to the nozzle 350 d. The nozzle 350 e, however, only providesthe central passage 724 between the plenum 338 and the chamber volume110.

FIG. 7F illustrates another embodiment of the nozzle, a nozzle 350 f,that is similar to the nozzle 350 c. The nozzle 350 f, however, has amounting portion 717 and a gas delivery portion 732 that is at anoblique orientation to the mounting portion 717. The nozzles 350 a-350 fhave been found to run cleaner (i.e., with reduced processing byproductbuildup) than conventional nozzles due to the proximity to the plasmathereby making the nozzles hotter and discouraging deposition ofreaction by-products. Because the gas delivery configuration of thenozzles minimizes flow recirculation within the chamber, the amount ofreaction by-products drawn towards the upper regions (i.e., the lidarea) of the chamber are reduced.

Common to the nozzles described above is that they have low thermal massand are not provided with cooling mechanism. Consequently, they heat upduring processing to a temperature above that of the cooled lid andliners, so as to thermally differentiate the nozzles from the lid andliners.. This helps to dramatically reduce polymer deposition on thenozzles. Optionally, in order to ensure that any polymer that does getdeposited on the nozzles, they are provided with surface roughness bybid blasting or by a chemical process.

Additional alternative embodiments of the gas distribution system areillustrated in FIGS. 8-13. In FIGS. 8-13, in lieu of nozzles 350,mini-gas distribution plates 220 having plural gas injection holes 225are provided in center section 310 of liner 134 to fluidly couple plenum338 and the chamber volume 110. Like nozzles 350, the area of each ofthe mini-gas distribution plates 220 facing the plasma is limited sothat: (1) the area is contained within a region in which the turbulencefrom the injected gas in the vicinity of the inlets prevents or impedespolymer accumulation, and (2) the size or thermal mass of the mini-gasdistribution plate is sufficiently low to allow rapid plasma-heating ofthe plate. In order to enhance the gas turbulence across the area of themini-gas distribution plate 220, the gas injection holes 225 in eachmini-gas distribution plate 220 are angled relative to the surface ofthe plate facing the chamber interior. Preferably, the gas injectionholes are angled so that the gas injection streams from adjacent holescross one another or together form a vortex pattern. In an alternativeembodiment of the placement of the mini-gas distribution plates 220, themini-gas distribution plates 220 extend slightly out from top linersurface 316 to enhance plasma-heating thereof and to enhance gasinjection turbulence. Preferably, the mini-gas distribution plates 220are each a relatively small fraction of the area of the entire ceiling316.

Each mini-gas distribution plate 220 is formed of a semi-metal such assilicon or a dielectric such as silicon dioxide (quartz) or sapphire,or, alternatively, of a non-conductive material or of a materialcompatible with processes conducted within processing chamber 100. Eachmini-gas distribution plate 220 has plural gas inlets 225 through whichprocess gas is sprayed into the reactor chamber interior. Preferably,the mini-gas distribution plates 220 are thermally insulated from thetemperature controlled liner 134, so that they are readily heated by theplasma within the chamber. Each gas distribution plate 220 issufficiently small relative to the ceiling—has a sufficiently smallthermal mass—so as to be rapidly heated by the plasma upon plasmaignition. (For example, the first liner 134 may have a diameter in arange of 9 inches to 14 inches, while a gas distribution plate 220 hasan exposed diameter on the order of about 0.25-0.5 inch. As a result,the plasma heats each mini-gas distribution plate 220 to a sufficientlyhigh temperature to prevent any accumulation of polymer thereon. Theadvantage is that the gas inlets 225 of each mini-gas distribution plate220, like the inlets of nozzles 350, can be kept clear of polymer.

Preferably, the diameter of each mini-gas distribution plate 220 issufficiently small so that the entire bottom surface 220 a of the gasdistribution plate 220 is enveloped within a region of gas flowturbulence of the process gas spray from the inlets 225. Thus, forexample, each mini-gas distribution plate 220 has an exposed diameter onthe order of about 0.25-0.5 inch. This region has sufficient gasturbulence to retard or prevent the accumulation of polymer on thesurface 220 a.

Referring to FIGS. 9 and 10, the gas turbulence around the bottomsurface 220 a is enhanced by introducing a crossing pattern of gas spraypaths from the plural gas inlets 225 of the mini-gas distribution plate220. The embodiment of FIGS. 9 and 10 provides a vortex pattern(indicated by the arrows of FIG. 9). This is accomplished by drillingeach of the gas inlets 225 at an angle A (as illustrated in FIG. 10)relative to the outlet surface 220 a of the mini-gas distribution plate220. Preferably, the angle A is in the range of about 20 degrees to 30degrees. In an alternative embodiment illustrated in FIG. 11, the gasspray paths of the plural gas inlets 225 are directed at other inlets inorder to enhance the gas turbulence. This alternative spray pattern isillustrated by the arrows in FIG. 11.

As a further aid in inhibiting the accumulation of polymer on themini-gas distribution plates 220, the outlet surface 220 a of the plate220 extends slightly below the surface of the ceiling 210 by a distanced, as shown in FIG. 12. The distance d is preferably about 0.02 inch to0.03 inch or a fraction of the thickness of the gas distribution plate220. The enlarged cross-sectional view of FIG. 12 illustrates oneexemplary implementation in which the gas inlets 225 are angled holespassing entirely through the mini-gas distribution plate 220. Processgas is supplied to the gas inlets 225 by a common manifold 230 formed inthe ceiling 316. A water jacket 240 of the water-cooled ceiling 316 isalso shown in the drawing of FIG. 12. Preferably, a thermal insulationlayer 250, which may be aluminum nitride for example, is trapped betweenthe mini-gas distribution plate 220 and the ceiling 316.

In an embodiment where controlled polymer accumulation is desired suchas an oxide etch process for example, the first liner 134 is maintainedat a sufficiently low temperature so that polymer accumulates on theexposed surfaces of the first liner 134 as a very hard film which isvirtually immune from flaking or contributing contamination to thechamber interior. The thermally differentiated mini-gas distributionplates 220 and nozzles 350 are heated by the plasma to a sufficientlyhigh temperature to inhibit accumulation of polymer thereon. Thus, thegas inlets 225 are kept clear of any polymer. The small size of themini-gas distribution plates 220 and nozzles 350 enables the plasma toefficiently heat them to a temperature above a polymer depositiontemperature. The small size also permits the concentration of gas inletsover the small surface 220 a to provide sufficient gas turbulence tofurther inhibit the accumulation of polymer on the surface 220 a, inlets225, or nozzles 350. The gas turbulence is enhanced by providing acrossed or vortex pattern of gas spray paths from each of the gas inlets225 of the mini-gas distribution plate 220, and having the outletsurface 220 a below the ceiling 316.

Another advantage of the minimized size nozzle is that because thenozzles size is small relative to the temperature controlled lid, plasmaformed in the processing volume will likely contact the temperaturecontrolled lid surface thereby improving byproduct adhesion to the lidas described above. The combination of all of the foregoing featuresprevents any observable accumulation of polymer on any portion themini-gas distribution plate 220 or the various nozzle embodiments.

FIG. 8 illustrates an embodiment where there are four mini-gasdistribution plates 220 mounted on the first liner 134 at foursymmetrically spaced locations overlying the periphery of the wafer 10.FIG. 8 also illustrates a plurality of semi-spherical bumps formed onthe surface of the ceiling. These bumps are about 0.5 to about 1.5 mmhigh and are spaced about 1 mm apart. Bumps 300 are yet anotheralternative embodiment of the chamber surface texturing described inmore detail below in the next section entitled “Chamber SurfaceAlterations to Improve Adhesion”. Of course, additional mini-gasdistribution plates 220 or nozzles 350 may be provided in otherembodiments, or their placement modified from the arrangementillustrated in FIGS. 4 and 8.

IV. Chamber Surface Alterations to Improve Adhesion

Another advantage of the present invention is the use of chamber surfacetopography to improve the adhesion of by products deposited on chambersurfaces. For example, in a conventional fluorocarbon based plasma etchof oxide features, polymeric byproduct formation is common. Referring toFIG. 2, for example, by-product deposition would occur on the surfacesof the two liners 118, 134 and lid 102 exposed to the plasma 148. Afterthe deposits accumulate to a certain thickness, the deposits will beginto flake off the lid and the chamber liners, thereby contaminating thesemiconductor devices being fabricated.

It is believed this aspect of the present invention further improvesadhesion of reaction byproducts or other material deposited on surfaceswithin the process chamber that are exposed to process gases, therebyallowing the chamber to be operated for longer time intervals betweencleaning such surfaces. Moreover, the improved byproduct adhesioncapability promotes the use of expanded process gascompositions-including those with high rates of byproduct formation.Specifically, chamber interior surfaces such as the surface of thetemperature controlled liner and lid, are fabricated with a surfacecontour or “texture” having topographical features—i.e., alternatingprotrusions and depressions (peaks and troughs)—whose width, spacing,and height dimensions are between 100 microns (0.1 mm) and 100 mm, andpreferably in the range of 500 microns (0.5 mm) to 8000 microns (8 mm).In contrast, the average roughness of surfaces treated by conventionalbead blasting is about 4 to 6 microns (0.15 to 0.23 mil), which is atleast 16 times smaller than the features of the invention.

By “topographical feature” or “elevation feature” of the surface we meanan area whose elevation deviates from the average surface elevation. Atopographical feature can be either a convex protrusion or a concavedepression. The “height” of a feature is the peak-to-trough deviation inelevation. If the feature is a concave depression, the “height” of thefeature is the depth of the depression.

It is believed that our textured surface improves adhesion of thedeposited material for at least two reasons. One reason is that verticalcontours (contours perpendicular to the average surface plane) increasecompressive forces within the deposited film in a direction normal tothe surface, thereby resisting cracking of the film due to thermalexpansion and contraction. A second reason is that a textured surfacehas a greater surface area for the material to bond to than a flatsurface.

The surface area increases in proportion to the depth of the depressionsor the height of the protrusions. While increasing the height dimensionin order to increase the surface area by improves adhesion of depositedmaterial, increasing the height beyond a certain value can becomedisadvantageous. First, an excessive height dimension can make thetextured surface harder to clean. Secondly, if the textured surface is athin, removable chamber lid or liner rather than a comparatively thickchamber wall, an excessive height dimension can reduce the strength andrigidity of the lid or liner, making it more susceptible to accidentaldamage.

The texturing of our invention can be applied to the surface of anycomponent of the process chamber. (By “component” we mean any object inor on the chamber.) The texturing preferably should be applied to anylarge surface that is exposed to the process gases in the chamberinterior and that is either above or near the wafer. The chambersurfaces for which it is most important to provide the texture of theinvention typically are the lower surface of the chamber roof (i.e.,interior surfaces of the chamber lid 102) and the liners 134 and 118.Since the chamber roof is directly above the wafer being processed, anyparticles that flake off of the roof probably will fall on the wafer,thereby causing a defect in the wafer. Since the chamber side wall orlining is very close to the perimeter of the wafer, there also is a highrisk that particles flaking off the side wall or lining will fall on thewafer. It is much less important to provide textured surfaces on chambercomponents positioned below the wafer, since particles flaking off ofsuch surfaces are unlikely to deposit on the wafer.

Different shapes and dimensions of depressions and protrusions in theexposed surfaces of the chamber roof and side wall lining were tested.All shapes tested greatly improved adhesion of deposited materialcompared with either smooth, untreated surfaces or surfaces roughened bybead blasting.

Viewed in conjunction with FIG. 4, FIGS. 13 and 14 are top and sectionalviews, respectively, of a portion of the lower surface 316 of a liner134 having a texture 60 consisting of a 2-dimensional array of squareprotrusions 60. For clarity, apertures 348 and nozzles 350 have beenomitted. The protrusions have height H, width W, and spacing S betweenadjacent protrusions. FIG. 15 shows a texture 60 a in which thetopographical features are square depressions into the surface ratherthan protrusions, and in which the sides of the square depressions areformed at an oblique angle θ relative to the horizontal surface betweenthe depressions, so that each depression is shaped as an inverted4-sided pyramid with a flat bottom rather than a sharp apex. FIGS. 16and 17 are top and sectional views of an alternative texture 1605 inwhich the depressions are rounded or hemispherical in shape.

FIGS. 18 and 19 are perspective and sectional views, respectively, of atexture consisting of a plurality of circumferential grooves 1805 in aliner 118.

FIG. 20 is a perspective view of a liner 118 having both circumferential1805 and longitudinal 1810 grooves.

While each topographical feature has been characterized as either aprotrusion or a depression, it is equivalent to consider the areabetween the depressions to be protrusions on the surface. In otherwords, it is arbitrary whether the protrusions or the depressions aredesignated as the topographical features. Therefore, referring forexample to FIG. 17, the spacing S between depressions or protrusionspreferably should be the same order of magnitude as the width W. Morepreferably, the spacing S and width W should differ by a factor of 2 orless. Similarly, the height H preferably should be the same order ofmagnitude as the width W and spacing S, and more preferably should bewithin a factor of 2 of those other two dimensions.

In any of the embodiments, we expect the adhesion of the deposited filmto the textured surface will maximized if there are no sharp corners inthe textured surfaces of the chamber components, because sharp cornersgenerally increase stress in the film. Consequently, the edges of thetopographical features should have rounded corners, with as high aradius of curvature as practical. Preferably, the radius of curvatureranges from between 130 microns (0.13 mm) to about 500 microns (0.5 mm).

Test Results

Control

We tested the invention by using a plasma etch chamber to perform aplasma process for etching films of silicon dioxide on silicon wafers,using a conventional fluorocarbon etchant gas mixture including C₄F₈ andCO. For the control, the process chamber had an aluminum nitride ceramicroof and an anodized aluminum side wall liner, both of which were smooth(i.e., had no surface texture treatments to improve adhesion.)

The etching process produces fluorocarbon reaction products which formpolymer films on exposed inner surfaces of the chamber roof and sidewalls. We found that, with conventional smooth roof and side wall liner,the polymer deposited on these surfaces began flaking off after thepolymer film reached a thickness of 0.6 to 0.65 mm. The thickness atwhich flaking occurred was independent of changes in process parameters.

EXAMPLE 1

Pyramid Depressions in Aluminum Nitride Roof

We fabricated a chamber roof (gas distribution plate) as a circular diskof aluminum nitride ceramic, 0.5 inch (13 mm) thick, in which we dividedthe lower circular surface of the roof (the surface exposed to thechamber interior) into four quadrants, with four different surfacetextures fabricated in the four quadrants. The first quadrant wassmooth, and the second quadrant was bead blasted with silicon carbideparticles.

The third and fourth quadrants both had the pyramid texture 60 a shownin FIG. 15, with bead blasting subsequently applied to the fourthquadrant but not the third. The dimensions of the pyramid features were:angle θ=45°, height H=0.6 mm, width W=1.5 mm, spacing S=0.6 mm. Wecalculate that the third quadrant had a surface area 30% greater thanthat of the first quadrant due to its pyramid texture.

Table 1—Example 1

Quadrant Pyramid Texture Bead Blasting 1 No No 2 No Yes 3 Yes No 4 YesYes

We expect that a pattern of square depressions or protrusions 60 asshown in FIG. 14 would be preferable to the pyramid-shaped depressionsactually tested, because the square features have a greater surfacearea. As stated earlier, we expect that maximizing the surface area ofthe surface contour is advantageous in order to maximize the adhesion ofthe material deposited thereon.

We installed the roof in a conventional plasma etch chamber andperformed the same plasma etch process performed in the Control. Wefound that the third quadrant of the roof exhibited the best polymeradhesion. Compared to the smooth first quadrant, we were able to process2.5 times more wafers before material deposited on the third quadrantbegan flaking. At this point, the polymer layer deposited on the thirdquadrant had a thickness of 1.2 mm, which is 85% thicker than themaximum polymer thickness that could be deposited on a conventionalsmooth or bead blasted surface without flaking.

Because bead blasting conventionally had been used to improve adhesionof deposited material, we were surprised to observe that bead blastingthe pyramid textured surface was detrimental to adhesion. Specifically,when we halted the test after depositing 1.2 mm of polymer on the lid,we observed a small amount of flaking from the fourth quadrant, and noflaking whatsoever from the third quadrant. We surmise that the beadblasting created sharp corners in the surface of the roof that increasedstress in the polymer film, thereby promoting cracks in the film.

Example 2

Different Pyramid Dimensions in Aluminum Nitride Roof

A second aluminum nitride roof (gas distribution plate) was fabricatedas described for Example 1. The four quadrants were textured withpyramids having different dimensions, as summarized in Table 1. In thefirst quadrant, the pyramid dimensions were identical to those ofquadrant 3 of Example 1. In the other three quadrants, the height H ofthe pyramid depressions was increased to 1.1 mm. In quadrants 3 and 4,the angle θ of the pyramid walls relative to the horizontal surface wasdecreased to 30°. In quadrants 2 and 4, the width W and spacing S wereincreased to 2.5 mm and 1.0 mm, respectively. All four quadrantsexhibited no flaking of the polymer deposits.

Table 2—Example 2

uadrant Angle θ Height H Width W Spacing S 1 45° 0.6 mm 1.5 mm 0.6 mm 245° 1.1 mm 2.5 mm 1.0 mm 3 30° 1.1 mm 1.5 mm 0.6 mm 4 30° 1.1 mm 2.5 mm1.0 mm

Example 3

Hemispherical Depressions in Aluminum Oxide Roof

We fabricated a roof of a 0.5 inch (13 mm) thick plate of aluminum oxide(alumina) ceramic. Alumina has a much lower thermal conductivity thanaluminum nitride, but it has the advantage of being readily machinable.We created the pattern of depressions shown in FIGS. 16 and 17 bydrilling in the alumina an array of approximately hemispherical holes,or holes having an arcuate cross section, having a hole diameter W of 4mm and a spacing S between the perimeters of adjacent holes of 1 mm. Wetested two prototypes in which the depth of the holes (the topographicalfeature height H) were 1 mm and 2 mm, respectively. Both prototypesexhibited no flaking of the polymer deposits.

Example 4

Square Protrusions in Anodized Aluminum

FIGS. 13 and 14 show an aluminum roof in which we machined an array ofsquare protrusions. While the section is illustrated as solid the samefeatures or protrusions may be incorporated into the top ceiling 316having a plurality of gas inlets 350 or mini-gas distribution plates220. The aluminum was anodized after the machining. In one prototype theprotrusions had 1 mm width W, 1.5 mm height H, and 3 mm spacing S. In asecond prototype, the protrusions had 2 mm width W, 2 mm height H, and 5mm spacing S. Both prototypes exhibited no flaking of the polymerdeposits.

In the second prototype, we also tested an implementation of the gasinlet holes in the gas distribution plate. Instead of a conventionalarray of gas inlet holes uniformly distributed over the surface of theplate, we installed in the plate only eleven quartz discs (not shown),where each quartz disc was 10 mm diameter and included eleven gas inletholes 0.6 mm diameter.

Example 5

Grooves in Anodized Aluminum

FIGS. 18 and 19 are perspective and sectional views, respectively, of acylindrical side wall liner 118 composed of anodized aluminum in whichwe machined a series of circumferential grooves 1805 using a lathe. Eachgroove had 1 mm width and 1 mm depth, and adjacent grooves were spacedapart along the axis of the cylindrical liner by 3 mm. The aluminum wasanodized after the machining.

FIG. 20 is a perspective view of a similar cylindrical liner having bothcircumferential 1805 and longitudinal 1810 grooves of the same width,depth, and spacing dimensions stated in the preceding paragraph.

Both prototypes exhibited no flaking of the polymer deposits. However,the FIG. 20 embodiment is expected to provide superior adhesion becauseits surface area is greater than that of the embodiments illustrated inFIGS. 18 and 19.

An advantage of the embodiments of FIGS. 18, 19 and 20 is that machininggrooves in aluminum typically is less expensive than the otherfabrication methods described earlier.

While the different textures may be illustrated and described withregard to first liner 134 or second liner 118, it is to be appreciatedthat the textures described herein may be applied to either or bothliners 134, 118. In alternative embodiments, liner 134 may have adifferent surface treatment than liner 118. In one specific embodiment,liner 134 may have texture 1605 while liner 118 has circumferentialgroove texture 1805.

V. Plasma Confinement

Another aspect of the byproduct management feature of the presentinvention is the use of a plasma confinement system to contain theplasma in the processing region 112. Containing the plasma within theprocessing region 112 helps prevent byproduct accumulation in thepumping volume 114. Reducing or eliminating byproduct accumulation inpumping volume 114 reduces the likelihood that byproduct deposition willoccur in and potentially damage pump 109. The plasma confinement featureof the present invention may be better appreciated through reference toFIG. 21.

FIG. 21 is an enlarged partial view of the etched chamber 100 of FIG. 1.Lid 102 has been removed for clarity. A vacuum pump 109 exhausts gasesfrom the processing volume 112 through annular exhaust manifold andcylindrical pumping channel 138 so as to reduce the total gas pressurein the chamber to a level suitable for the plasma process intended to beperformed in the chamber. A throttle valve 8 is mounted within thepumping volume 114. The throttle valve 8 regulates the gas pressurewithin the chamber by controlling the impedance to gas flow within thepumping channel 138, thereby controlling the pressure drop across thepumping channel as required to maintain the desired chamber pressure.

While described as separate liners, it is to be appreciated that liners36 and 38 could be combined into a single liner such as described abovewith regard to liner 118. It is to be appreciated that each of theplasma confinement features described herein with regard to liners 36,and 38 apply to liner 118. It is to be further appreciated that liners36 and 38 are equipped with internal conduits such as conduit 119 ofliner 118 for circulating temperature controlled fluid as describedabove with regard to FIG. 6 and liners 118 and 143.

The inner liner 38 and the lower half of the outer liner 36 respectivelyfunction as the inner and outer walls of the annular exhaust volume 114.The annular flange 40 at the bottom of the inner liner 38 includes anarcuate aperture 42, aligned with the cylindrical pumping channel 138,to permit exhaust gases to flow from the annular exhaust manifold,through the flange aperture 42, and then through the cylindrical pumpingport 138 to the throttle valve 8 and the pump 109.

The exhaust channel of the illustrated chamber includes an annularexhaust manifold and a cylindrical pumping channel. The annular exhaustmanifold is coaxial with the chamber interior and extends around all ormost of the azimuth of the chamber interior. The cylindrical pumpingchannel is coupled to the exhaust manifold at one azimuthal position.Some conventional plasma chambers include an annular exhaust manifoldcoupled directly to the exhaust pump without any intermediate pumpingchannel. Other conventional plasma chambers couple the pump to thechamber interior using only a pumping channel that does not extendaround the azimuth of the chamber interior. In this patentspecification, the term “exhaust channel” or “exhaust passage”encompasses either an annular exhaust manifold or a pumping channel, orthe two in combination.

Exhaust Channel and Magnet for Confining Plasma

An exemplary embodiment of the invention, shown in FIGS. 21-23, employstwo features—a gas flow deflector 522, 516 and a magnet system 50—thatoperate synergistically to prevent the plasma body within the chamberinterior from reaching the exhaust pump. In addition to its beneficialfunctions as detailed below, this arrangement assists in providing highpumping capacity while avoiding polymer deposition in the pumpingsystem. That is, as explained in the present disclosure, one feature ofthe inventive chamber is the high flow pumping capability for reducedresidence time of the gas molecules. However, for maintenance reasons,it is advisable to constrain or limit the plasma from reaching to thepumping area of the chamber. The arrangement described below assists inachieving this goal.

Specifically, the interior of the exhaust manifold 30 includes at leastone deflector 522, 516 that deflects at least a substantial portion ofthe exhaust gases transversely, instead of allowing all of the exhaustgases to flow in an unobstructed straight path through the exhaustmanifold. (By “transversely” we mean perpendicular to the direction ofthe path along which the gases would flow in the absence of thedeflector.)

The deflector creates turbulence in the flow of exhaust gases thatincreases the rate of collisions of reactive species in the gases withthe deflector and with the walls of the exhaust manifold near thedeflector. The collisions promote surface reactions among the reactivespecies so as to produce deposits on the walls. This depletes theexhaust gases of the reactive species that tend to produce suchdeposits, thereby greatly reducing or eliminating the concentration ofsuch reactive species in the exhaust gases downstream of the deflector,and therefore greatly reducing or eliminating undesirable deposits onthe throttle valve 8 and pump 109.

The deflector also increases the rate of collisions of charged particlesin the exhaust gases so as to promote recombination of such chargedparticles, thereby reducing the concentration of charged particles inthe exhaust gases.

Additionally, a magnet system 50 (52-57) is positioned near thedeflector 522, 516 so as to produce a magnetic field within the exhaustmanifold near the deflector. The magnetic field preferably has asubstantial component directed transverse to the direction of exhaustgas flow through the manifold. The transverse component of the magneticfield transversely deflects moving electrons so that they are morelikely to recombine with positive ions, thereby reducing theconcentration of charged particles in the exhaust gases.

Since the deflector and the magnetic system both reduce theconcentration of charged particles in the exhaust gases, the two incombination can reduce the concentration sufficiently to extinguish theplasma downstream of the deflector and magnet system. Specifically, themagnetic field should be strong enough, and the turbulence caused by theone or more deflectors should be great enough, so that the combinedeffects of the magnetic field and the deflector prevent the plasma bodywithin the chamber from reaching the throttle valve 8 and exhaust pump109.

The plasma confinement effect of the magnetic field permits the use of awider and/or less sinuous exhaust channel than would be required toblock the plasma without the magnetic field. Therefore, the pressuredrop across the exhaust channel can be reduced in comparison with priorart designs that rely entirely on the sinuousness of the exhaustmanifold to block the plasma.

In the embodiment shown in FIGS. 21-23, the deflector consists of twocoaxial, annular protrusions 522, 516 extending into the gas passagewayof the exhaust manifold 30 from the walls of the manifold. The upperprotrusion 522 extends radially inward from the outer liner 36, and thelower protrusion 516 extends radially outward from the inner liner orcathode shield 38. Because the two protrusions overlap each otherradially, they do not permit any of the exhaust gases to travel in astraight line through the exhaust manifold, thereby maximizing thelikelihood that reactive species in the exhaust gases will collide witheither the protrusions or the walls of the exhaust manifold.

We define a “magnet system” as one or more magnets in combination withzero, one or more magnetically permeable pole pieces to form a magneticcircuit having a north pole and a south pole. In the embodiment of FIGS.21-23, the magnet system 50 consists of two annular magnets 52, 53mounted coaxially with the annular exhaust manifold 30 and spaced apartalong the axis of the manifold. The two annular magnets are identical,except that the first magnet 52 has its north and south poles at itsradially inner and outer ends, respectively, whereas the second magnet53 has its north and south poles at its radially outer and inner ends,respectively. The magnet system 50 also includes a cylindrical,magnetically permeable pole piece 54 mounted coaxially with the twomagnets 52, 53 so as to abut and extend between the radially inner endsof the two magnets, thereby completing a magnetic path or “magneticcircuit” between the two magnets.

Consequently, the north pole 56 of the magnet system 50 is the northpole of the first annular magnet 52, i.e., the pole of the first magnetopposite the pole that abuts the pole piece 54. The south pole 57 of themagnet system 50 is the south pole of the second annular magnet 53,i.e., the pole of the second magnet opposite the pole that abuts thepole piece 54.

The magnet system 50 preferably is mounted within the lower protrusion516 so that the ends of the north and south poles 56, 57 of the magnetsystem are as close as possible to the narrow portion of the gaspassageway within the exhaust manifold that is radially outward of theprotrusion. Mounting the magnet system close to the narrowest portion ofthe exhaust manifold passageway is desirable to maximize the magneticfield strength to which the exhaust gases are subjected.

An exemplary implementation of the magnet system just described has aU-shaped cross section as shown in FIGS. 21-23, with the base of the “U”pointing radially inward and the open end of the “U” pointing radiallyoutward. More specifically, the shape of the magnet system is that of aU-shaped horseshoe magnet that is revolved around the longitudinal axisof the chamber.

The magnetic field pattern produced by this U-shaped magnet system,represented by field line 58 in FIG. 22, is desirable because it isconcentrated primarily within the passageway of the exhaust manifold.This concentration has at least two advantages. One advantage is that,as stated above, it maximizes the magnetic field strength to which theexhaust gases are subjected, thereby maximizing the effectiveness of themagnet in extinguishing the plasma downstream of the magnet.

A second advantage of the U-shaped magnet system is that the magneticfield strength declines rapidly along the longitudinal axis of thechamber, so that the magnetic field strength is low at the workpiece 10.To minimize the risk of damaging the workpiece by ion bombardment orelectrostatic charge accumulation, the magnetic field strength at theworkpiece 10 should be as low as possible, preferably no greater than 5gauss, and more preferably no greater than 3 gauss. The magnet system ismounted in the lower protrusion 516 rather than the upper protrusion 522in order to position the magnet system as far as possible from theworkpiece 10, thereby minimizing the strength of the magnetic field atthe workpiece 10.

FIG. 24 shows an alternative magnet system 60 whose magnets and polepieces are interchanged relative to the embodiment of FIGS. 21-23.Specifically, the upper and lower annular members 62, 63 aremagnetically permeable pole pieces rather than magnets. The cylindricalmember 64 is a magnet rather than a pole piece, the cylindrical magnethaving a north magnetic pole at the upper end of its longitudinal axisabutting the upper pole piece 62 and a south magnetic pole at the lowerend of its axis abutting the lower pole piece 63.

A possible alternative implementation of the exhaust manifold could omitthe upper protrusion 522, relying on the combination of the lowerprotrusion 516 and the magnet system 50 to block the plasma.

Another alternative exhaust manifold design would omit the lowerprotrusion 516 (which extends radially outward from the inner liner 38)and substitute a modified magnet system 51, shown in FIG. 25, that ismounted within the upper protrusion 522 (which extends radially inwardfrom the outer liner 36). The north and south magnetic poles 56, 57 ofthe modified magnet system 51 should be adjacent the gas passageway atthe radially inner end of the protrusion 44. This can be accomplishedusing the same magnets 52, 53 and pole piece 54 as in the FIG. 23 magnetsystem, but with the pole piece 54 moved from the radially inner end tothe radially outer end of the two magnets, as shown in FIG. 25.

FIG. 26 shows an alternative magnet system 61 that differs from the FIG.25 magnet system 51 in that the magnets and pole pieces areinterchanged. (See the discussion of the FIG. 24 embodiment above.)

We also tested the exhaust manifold design shown in FIG. 27 in a plasmachamber that otherwise was identical to the chamber shown in FIG. 21.The exhaust manifold of FIG. 27 includes upper and lower annular magnets68, 69 mounted within the upper and lower protrusions 522, 516,respectively, of the exhaust channel 30. The upper magnet 68 has northand south poles at its radially inner and outer ends, respectively. Thelower magnet 69 has north and south poles at its radially outer andinner ends, respectively. Consequently, the north and south poles of theupper magnet are aligned with the south and north poles of the lowermagnet. The resulting magnetic field, depicted by magnetic field lines70, is highly concentrated in the region of the exhaust manifold channelor passageway between the two protrusions. As explained in the precedingdiscussion of the FIG. 21 embodiment, such concentration is desirable tomaximize the strength of the magnetic field to which the exhaust gasesare subjected and to minimize the magnetic field at the workpiece 10.

To facilitate testing the FIG. 27 embodiment with different gaps betweenupper and lower protrusions 522, 516, our prototype included an annulardielectric spacer 72 below the outer dielectric liner 36. Bysubstituting a thicker spacer 72, we could increase the height of theupper protrusion 522 and thereby increase the gap between the twoprotrusions. We used the same magnets 68, 69 for every spacer thicknesswe tested. Therefore, when we substituted a thicker spacer, we bothincreased the gap and decreased the magnetic field strength in the gap.

In these tests we found that the plasma was successfully blocked fromextending below the lower protrusion when the gap between the upper andlower protrusion was 0.5 inch or less and the magnetic field strength inthe gap was at least 100 or 150 gauss. We also found that, in theillustrated chamber, the magnetic field strength declined fast enoughaway from the magnets so that the magnetic field strength at theworkpiece 10 was less than 3 gauss, which we consider low enough toavoid risk of damage to the workpiece. However, when we tested a widergap between the two protrusions, and therefore a lower magnetic fieldstrength in the gap, we found that the plasma was not successfullyblocked.

We currently prefer the FIG. 21 embodiment because more manufacturinglabor is required to mount magnets within two protrusions as in the FIG.27 design in comparison with mounting magnets in only one protrusion asin the FIG. 21 design.

Another alternative embodiment of the exhaust manifold would be to omitone protrusion and its corresponding magnet from the FIG. 27 embodiment.We tested a prototype that was identical to the one shown in FIG. 27,except that the upper protrusion 522 and the upper magnet 68 was omittedleaving only the lower protrusion and magnet as illustrated in FIG. 28.While this prototype successfully, blocked the plasma from extendingbelow the lower protrusion, we considered the magnetic field at theworkpiece to be undesirably strong. However, this embodiment might besuitable for use in semiconductor fabrication processes in which theworkpiece is not overly susceptible to damage by ion bombardment orelectrostatic charge accumulation.

More generally, the deflector 522, 516 need not be one or moreprotrusions extending from the walls of the exhaust channel, but can beany structure within the exhaust channel that causes substantialturbulence in the exhaust gases. As described earlier, such turbulencewill promote recombination of charged particles so as to help extinguishthe plasma downstream of the turbulence, and it will promote surfacereactions among reactive species so that reaction products will bedeposited on surfaces near the deflector rather than on pumpingcomponents 8, 109 downstream.

The deflector and magnet system can be mounted in any part of theexhaust channel, such as the pumping channel 32, even though they aremounted in the annular exhaust manifold in the preferred embodiment.

Of course, any materials between the magnet system and the interior ofthe exhaust channel should be non-magnetic so as to avoid blocking themagnetic field from reaching the exhaust gases. As stated earlier, inthe preferred embodiment the protrusions in which the magnet system ismounted are anodized aluminum.

To equalize the exhaust gas flow rate around the azimuth of the chamber,it is preferable to slightly reduce the radial width of the exhaustmanifold near the azimuth of the pumping channel and to slightlyincrease its radial width near the opposite azimuth, i.e., near theazimuth 180 degrees away from the pumping channel.

The directions of the magnetic fields can be reversed without affectingthe operation of the invention. Therefore, all references to north andsouth poles can be interchanged.

The illustrated plasma chamber has circular symmetry because it isintended for processing a a single, circular semiconductor wafer. Inplasma chambers having other geometries, such as chambers for processingmultiple substrates or rectangular substrates, the components of theinvention such as the deflector and magnet system would be expected tohave rectangular or more complex geometries. The term “annular” as usedin this patent specification is not intended to limit the describedshape to one having a circular inner or outer perimeter, but encompassesrectangular and more complex shapes.

VI. Alternative Chamber Embodiments of the Present Invention

FIG. 28 is a cross sectional view of a capacitively coupled, MageticallyEnhanced Reactive Ion Etch (MERIE) chamber having embodiments of theimprovements of the present invention. FIG. 28 illustrates an etchprocessing system 2800 similar having the same systems as processingsystem 50 of FIG. 1. Etch processing system 2800 includes MERIE chamber2850. MERlE chamber 2850 is similar to chamber 100 described above withthe inclusion of a number of paired electromagnets. For example, fourelectromagnets 2810, 2812, 2814, and 2816, typically mounted in agenerally rectangular array, one each on the alternating walls ofchamber sidewall 106 each having a suitable power supply 2830, 2832,2834 and 2836. For clarity, only electromagnets 2810 and 2812 and theirrespective power supplies 2830 and 2832 are illustrated in FIG. 28.Under the control of controller 140, the coil pairs 2810 and 2812 and2814 and 2816 cooperatively provide a quasi-static, multi-directionalmagnetic field which can be stepped or rotated about the wafer 10.Electromagnets 2810, 2812, 2814 and 2816 generate a controllablemagnetic field with a magnitude from about 0 Gauss to about 150 Gauss.Also, the magnitude of the magnetic field can be adjusted to select etchrate and vary ion bombardment. Additional details of MERIE chamberoperation are provided in commonly assigned U.S. Pat. No. 4,842,683entitled, “Magnetic Field-Enhanced Plasma Etch Reactor.”

FIG. 28 also illustrates an alternative embodiment of the second liner118 having only the lower protrusion 516. Magnetic confinement system 52is disposed within lower protrusion 516. While the magnetic confinementsystem 52 is illustrated, it is to be appreciated that any of themagnetic confinement systems described above in the section entitled“Plasma Confinement” may be modified for use in the single protrusionembodiment of the liner 118.

FIG. 29 is a cross sectional view of another type of etch chamber havingembodiments of the present invention. FIG. 29 illustrates an etchprocessing system 2900 having an etch processing chamber 2950.Processing system 2900 is similar to processing system 50 of FIG. 1 withthe addition of a second RF generator 2910 and impedance matchingcircuits 2915. Processing chamber 2950 is similar to processing chamber100 with the addition of parallel plate 2920. In operation, RF signalsfrom RF generators 150 and 2910 are provided under the control ofcontroller 140, via impedance matching circuitry 151 and 2915,respectively, to electrode 105 and parallel plate electrode 2920,respectively. In one alternative embodiment, RF generators 150 and 2920provide RF signals at the same frequency. In an alternative embodiment,RF generators 150 and 2920 provide RF signals at different frequencies.

FIG. 30 is a cross sectional view of another processing chamberincorporating embodiments of the present invention. FIG. 30 illustratesan etch processing system 3000 having a magnetically enhanced etchchamber 3050. Processing system 3000 is similar to processing system 50with the addition of controller 140 operating a magnetic fieldgenerating mechanism 3010. Processing chamber 3050 is similar toprocessing chamber 100 with the addition of the magnetic fieldgenerating mechanism 3010. The magnetic field generating mechanism 3010is disposed on the outer peripheral surface of the cylindrical wall 106of the process chamber 3050. The magnetic field generating mechanism3010 comprises a plurality of circumfrentially arranged permanentmagnets having a predetermined polarity which enables generation of amagnetic field parallel to the upper surface of the wafer 10, and adriving mechanism for revolving the magnets around the processingchamber 3050. The magnetic field generating mechanism 3010 generates arotational magnetic field, which rotates about the vertical center axisof the process chamber 3050 or of the wafer 10, in the processing volume112 region. Additional details regarding the magnetic field generatingmechanism 3010 is disclosed in, for example, U.S. Pat. No. 5,980,687.

FIG. 31 is a cross sectional view of another processing chamberincorporating embodiments of the present invention. FIG. 31 illustratesan etch processing system 3100 having an etch chamber 3150. Processingsystem 3100 is similar to processing system 50 with the addition of asecond RF generator 3110 and impedance matching circuitry 3105 operatedby controller 140. Processing chamber 3050 is similar to processingchamber 100 with the addition of modifications to lid 102 to accommodateantenna 3115 mounted to the lid 102 and acting as an inductive memberfor coupling RF power from RF generator 3110 into processing volume 112.Impedance matching circuitry 3105 couples the RF signal from generator3110 to antenna 3115. Nozzles 350 have been positioned at the peripheryof lid 102 to accommodate the efficient inductive coupling of rf energyfrom antenna 3115 to a plasma formed in processing volume 112. FIG. 31illustrates antenna 3115 in a flat coil arrangement. Other arrangementsof antenna 3115 are possible, such as, for example, a ring arrangement,spiral arrangement, stacked arrangement, or, additionally, multipleantenna segments could be employed with each antenna segment of amultiple antenna segment coupled to an r.f. generator.

FIG. 32 is a cross sectional view of another embodiment of an etchchamber having the improvements of the present invention. FIG. 32illustrates an etch processing system 3200 having an etch chamber 3250.Processing system 3200 is similar to processing system 50 of FIG. 1 withthe addition of the second RF generator 3204 and impedance matchingcircuit 3206. Etch chamber 3250 is similar to etch chamber 100 with theaddition of a flat inductive coil 602 and a showerhead style gasinjection system instead of injector nozzles 350. The etch chamber 3250has a temperature controlled chamber liner 104 which regulates thetemperature of the chamber liner 104 in the manner described above. Thechamber 3250 has a lid assembly 3208 that, with the chamber walls 106and chamber bottom 108, define the process volume 110. A showerhead 3212is disposed beneath the lid assembly 3208. Process and other gases froma gas panel 105 pass through a passage in the lid assembly 3208 and aredispersed into the chamber volume 110 through a plurality of holes inthe showerhead 3212. Although shown with a first liner 118 and a secondliner 134, the etch chamber 3250 may comprise one or both of the firstand second liners 118 and 134. Etch chamber 3250 also illustrates aliner 118 having only a single protrusion 516 with magnetic system 50disposed therein.

VII. Chamber Process Window and Representative Critical Dielectric EtchProcesses

Embodiments of the improvements of the present invention provideexpanded dielectric etch processing capability. The dielectric etchprocess window enabled by combining the various improvements surpassesthe dielectric etch window enabled by conventional etch chambers.

For example, a magnetically enhanced reactive ion etch chamber havingembodiments of the present invention, such as, for example, MERIEchamber 2800 of FIG. 28, has several processing advantages overconventional MERIE processing reactors. Since it is not uncommon fordielectric etch processes to generate polymeric byproducts, severalaspects of the present invention cooperatively provide improved polymeradhesion control. First, direct temperature control liners on the wallsand cathode help minimize the heating effects caused by plamsa cycling.Plasma cycling occurs when the plasma heats portions of the chamberduring processing. Polymer adhesion generally decreases with increasingtemperature. As a result, those areas heated by plasma cycling are morelikely to have polymer depositions that tend to flake off and causeparticle contamination. By controlling and uniformly reducing thetemperature of the liners, adhesion of the polymeric byproducts to theliners is improved thereby reducing the likelihood that the polymerbyproducts will flake off and form particles. Second, use of minimizedsize gas inlet nozzles 350 ensures that the nozzles are heated by theplasma to temperatures above which the likelihood that by products willform on or adhere to the nozzle openings is reduced. Another advantageof minimized gas inlet nozzles 350 is that because of the small gasinlet nozzle area most of the plasma and by products contact thetemperature controlled lid. Like the byproducts that come into contactwith the temperature controlled liners, byproducts contacting thetemperature-controlled lid will also preferentially deposit on andadhere to the temperature controlled lid and not on the plasma heatedminimized size gas distribution nozzles. Third, the cathode and walltemperature controlled liners and the temperature-controlled lid mayalso further improve byproduct adhesion by incorporating surfacetexturing features such as those described above in Section IV. Thus,the combination of temperature controlled wall and cathode liners andtemperature controlled lid together with minimized gas inlets ensuresthat most of the plasma processing region comprises temperaturecontrolled surfaces with, preferably, high adhesion texturing.

Processing chambers having embodiments of the present invention enabledielectric etch processes employing high magnetic fields as high asabout 120 G and RF energy up to about 2500 W. Embodiments having a highchamber volume, such as a chamber volume of about 25000 cc, and highcapacity vacuum pumping systems such as, for example, a pump systemhaving a pumping speed of from about 1600 l/s to about 2000 l/s enable ahigh gas flow-low chamber pressure processing regime that is notavailable in conventional magnetically enhanced and reactive ion etchprocessing reactors. One advantage of the high pumping speed is animproved capability to control reactive species formation and residencetime. Residence time is directly related to the amount of reactive gasdissociation occurring in the plasma. The longer a gas molecule remainsexposed to a plasma, the more likely it is that dissociation of that gasmolecule will continue. Thus, etch processing reactors havingembodiments of the present invention provide desirable plasma gascompositions by enabling improved residence time control.

Attempts have been previously made and reported on the use of C₄F₆ fordielectric etch processes. However, these reports have taught away fromusing a parallel plate reactor, such as the reactor of the presentinvention, for dielectric etch using C₄F₆, especially for the linearform of C₄F₆, e.g., hexafluoro-1,3-Butadiene (CF2═CFCF═CF2). Moreover,for the best knowledge of the inventors, none of the reported attemptshave been successfully transferred into production lines.

For example, Yanagida discloses the use of a chain,hexafluorocyclobutene (c-C₄F₆), rather than linear (C₄F₆) in U.S. Pat.No. 5,338,399. On the other hand, in U.S. Pat. No. 5,366,590, Kadamurasuggests that either linear of chain C₄F₆ may be used, but that a highdensity plasma, such as that generated using ECR plasma source,inductively coupled plasma source, or transformer coupled plasma source,must be used with either gas. Similarly, in Japanese Application Hei9[1997]-191002 Fukuda discloses his work with linear C₄F₆, also usinghigh density plasma generated using ECR plasma source. Chattetjee etal., report their work with hexafluoro-2-buttyne andhexafluoro-1,3-Butadiene, also using high density plasma generated byinductively coupled plasma source. Evaluation of UnsaturatedFluorocarbons for Dielectric Etch Applications, Ritwik Chatterjee, SimonKarecki, Laura Pruette, Rafael Reif, Proc. Electrochem. Soc. PV 99-30(1999). Thus, the prior art teaches that in order to achieve acceptableetch results using linear C₄F₆, such as hexafluoro-1,3-Butadiene, oneshould use high density plasma, and not low or medium density plasma,such as that achieved using a capacitively coupled plasma source.

However, the present inventors have shown admirable results of etchingusing linear C₄F₆ in a capacitively coupled plasma source of theinvention. The present inventors believe that the high energy generatedby high density plasma chambers causes excessive dissociation of thelinear C₄F₆. Therefore, they believe that improved results can beachieved using a capacitively coupled chamber, so as to limit thedissociation of the molecules. Also, the present inventors further limitdissociation by using the high pumping capacity enabled by the inventiveetch chamber.

While not desiring to be bound by theory, it is believed that as anetchant gas, such as for example, linear C₄F₆, enters the plasma regionof a processing chamber and is exposed to the plasma, it is cracked ordissociated into smaller entities. Generally, for fluorocarbon processgases, shorter residence times provide a capability to produce anincreased percentage of the desirable fluorocarbon radical CF_(x)* whilelonger residence times produce an increased fraction of the fluorineradical F*. Too much fluorine radical production may reduce photoresistselectivity and/or reduce sidewall profile control. Applicants havefound that photoresist selectivity is generally improved with aresidence time of less than about 70 ms, and preferably a residence timeof less than about 50 ms. Applicants have found that oxide etch rate isimproved with a residence time of about 40 ms. Such residence time ismade possible by the processing reactor of the present invention andenables etching using linear C₄F₆ in a capacitively coupled RIE mode.

Another useful method of controlling the degree of radical formation ina gas composition is by incorporating an inert gas into the reactive gascomposition. It is believed that increasing the amount of inert gas in areactive gas composition reduces the amount of radicals formed from thereactive gas when the reactive gas/inert gas mixture is exposed to aplasma. Inert gas flow rate to reactive gas flow rate ratios from about5:1 to about 20:1 are preferred. Total gas flows from about 50 sccm toabout 1000 sccm with inert gas flow to reactive gas flow ratios ofbetween about 12:1 to about 16:1 being more preferred.

Dielectric etch chambers having embodiments of the present inventionenable a dielectric etch process window comprising up to 2500 W RFpower, magnetic fields from about 0 to about 150 Gauss, total gas flowsfrom 40 sccm to 1000 sccm, chamber pressures from about 20 mT to about250 mT and liner temperatures ranging from about −20° C. to about 50° C.As described below with regard to FIGS. 33-38, the expanded processwindow enabled by etch reactors having embodiments of the presentinvention provide improved dielectric etch process performance,reliability and process tuning versatility for a wide variety ofcritical dielectric and oxide etch applications.

A representative self-aligned contact feature is illustrated in FIGS.33A and 33B, which are not to scale. FIG. 33A represents pre-etch selfaligned contact structure 3300. FIG. 33B represents post etchself-aligned contact structure 3305. Both self aligned contactstructures 3300 and 3305 are formed on a silicon substrate 3310.Generally, word lines 3315 typically comprise and oxide layer 3316, aWSi_(x) layer 3317 and a polysilicon layer 3318. Word lines 3315 arecovered by a liner layer 3320 that is typically formed from siliconnitride. A representative bitline region 3325 is illustrated betweenadjacent word lines 3315. Dielectric layer 3330 is formed over linerlayer 3320 and is typically formed from a silicon dioxide, such as, forexample, and oxide layer formed from O₃-TEOS based processes.Alternatively, the dielectric layer 3330 may be formed from a dopedsilicon oxide film, such as, for example, a boron and phosphorus dopedsilicon glass (BPSG). Self aligned contact feature 3300 may includeother layers, such as, for example, an anti-reflective coating may beutilized between pattern layer 3335 and dielectric layer 3330.

Also illustrated in pre-etch self-aligned contact feature 3300 of FIG.33A is a mask pattern layer 3335. When pre-etch self aligned contactfeature 3300 is exposed to a suitable etch process, dielectric layer3330 is etched thereby transferring the pattern of mask layer 3335 ontothe dielectric layer 3330. As illustrated in FIG. 33B, a contact area3340 is formed when a portion of dielectric layer 3330 adjacent contactregion 3325 is removed.

The exact dimensions of the self aligned contact structure 3300 and 3305will vary depending upon a number of considerations, such as forexample, device application, to design rules and critical dimensions ofcontact area 3340. For example, for purposes of illustration and notlimitation, the self aligned contact structure 3300 may be a 0.25 microndesign rule device having an overall dielectric layer 3300 thickness ofabout 6000 angstroms, a liner layer 3320 thickness of about 650angstroms and a mask layer 3335 thickness of more than about 7000angstroms with a pattern opening of about 0.25 microns. The self alignedcontact etch processes enabled by the present invention are capable ofetching self-aligned contacts having design rules with criticaldimensions of less than about 0.25 microns and preferably havingcritical dimensions of between about 0.1 microns and to less than about0.18 microns.

Etching of a self-aligned contact feature is a critical dielectric etchapplication in part because of the need to avoid etch stop or residualoxide at the word line sidewall. Additionally, a suitable self alignedcontact etch process must maximize selectivity to the nitride shoulder3345. Preferably, nitride shoulder selectivity is greater than about20:1.

A suitable self aligned contact etch process chemistry comprises afluorocarbon gas, and an oxygen comprising gas and an inert gas wherethe total gas flow is more than about 700 sccm and the inert gascomprises more than about 90% of the total gas flow. Reactive gas ratiorefers to the ratio of the inert gas flow to the reactive gas flow. Inthis example, reactive gas ratio would be the ratio of the inert gasflow rate to the combined gas flow rates of the fluorocarbon gas and theoxygen comprising gas. A suitable self-aligned contact etch process hasa reactive gas ratio of from about 12:1 to about 16:1 with a preferredreactive gas ratio of about 14.5:1. In a specific embodiment, the ratioof the flow rate of the fluorocarbon gas to the flow rate of the oxygencomprising gas is from about 1.5:1 to about 2:1. The chamber pressure ismaintained from about 30 mT to about 40 mT, RF power is maintained fromabout 1800 W to about 2000 W, the magnetic field is about 50 G and theetch chamber is exhausted at a rate of from about 1600 l/sec to about2000 l/sec. In a specific preferred embodiment, the etch chamber isexhausted at a rate of from about 48 chamber volumes to about 80 chambervolumes per second. In another preferred embodiment, the substratesupport or cathode is maintained at between about 15° C. to about 20° C.while the temperature of a wall or, preferably a temperature controlledliner adjacent the substrate is maintained at about 50° C. In aspecific, preferred embodiment the fluorocarbon gas is CF₄F₆, the oxygencomprising gas is O₂ and the inert gas is Ar.

A representative high aspect ratio dielectric etch process will now bedescribed with reference to FIGS. 34A and 34B. FIG. 34A illustrates apre-etch high aspect ratio structure 3400 and FIG. 34B illustrates apost etch high aspect ratio structure 3405. Neither structure 3400 nor3405 are illustrated to scale. In this context, a high aspect ratiodielectric etch process is defined as etching features having aspectratios greater than about 5:1 to about 6:1 while a very high aspectratio process is defined as etching features having aspect ratios in therange of from about 10:1 to about 20:1. For example, the aspect ratio ofthe feature 3430 in FIG. 34B is the ratio of the dielectric layerthickness 3422 to the feature width 3426. Magnetically enhanced andreactive ion etch chambers having embodiments of the present inventionare capable of etching both high and very high aspect ratio features.

Turning now to FIG. 34A, a representative pre-etch high aspect ratiostructure 3400 is illustrated that comprises a stop layer 3415 formedover a silicon substrate 3410. A dielectric layer 3420, having athickness 3422, is formed over the stop layer 3415. A mask layer 3425 isformed over the dielectric layer 3420. Stop layer 3415 could be formedfrom a suitable stop layer material, such as silicon nitride forexample. Of course, the specific type of stop layer material will dependupon the device type and design rules of a particular device.

FIG. 34B illustrates post etch high aspect ratio structure 3405comprising high aspect ratio feature 3430. High aspect ratio feature3430 is formed in the dielectric layer 3420 by transferring the patternof mask layer 3425 onto dielectric layer 3420. The pattern of mask layer3425 is transferred onto dielectric layer 3420 by conducting a suitablehigh aspect ratio dielectric etch process in and etch processing reactorhaving embodiments of the present invention as described in greaterdetail below. While a specific feature width 3426 will vary dependingupon design rules, in general, feature width 3426 varies from about 0.25micrometers to about 0.1 micrometers. The feature depth corresponds tothe thickness of dielectric layer 3420.

As dielectric layer thickness 3422 increases, the selectivity of thehigh aspect ratio dielectric etch process to the mask layer 3425photoresist material becomes even more critical. The possibility of etchstop also increases with increasing dielectric layer thickness 3422.Shrinking feature width 3426 also poses challenges for maintaining anappropriate sidewall profile of contact 3430. Bowing or a re-entrantsidewall profile of contact 3430 can lead to an unacceptably smalldiameter at the bottom of contact 3430 adjacent stop layer 3415. Highaspect ratio contact etching is a critical dielectric etch processbecause of the challenges posed by shrinking feature width, increasingcontact depth, selectivity to photoresist materials and sidewall profilecontrol.

High aspect ratio feature etching may also be complicated by adielectric layer 3420 comprising a doped silicon oxide such as, forexample, BPSG. Dielectric layers 3420 comprising a plurality ofdielectric materials forming a multilevel structure also pose manychallenges to high aspect ratio feature etching. One example of such amultilevel structure is a feature structure having a dielectric layer3420 comprising multiple intermediate stop layers at different depths,such as for example, those features seen mainly in the peripheral areasof stack capacitor DRAM structures.

The exact dimensions of the high aspect ratio structure 3400 will varydepending upon a number of considerations, such as for example, thedevice application, and the design rules of a particular device. Forexample, the representative high aspect ratio structure 3400 may have amask with 3426 of about 0.25 microns, a mask layer 3425 thickness ofabout 7000 angstroms, a dielectric layer thickness 3422 of about 15,000angstroms and a stop layer 3415 thickness of about 500 angstroms. It isto be appreciated that the above specific dimensions or for illustrationand not for limitation. Magnetically enhanced and reactive ion etchchambers having embodiments of the present invention are capable ofetching high aspect ratio and very high aspect ratio features havingaspect ratios from about 5:1 to about 20:1 with critical dimensions(i.e., contact with 3426, for example) of from about 0.25 microns toabout 0.1 microns.

Suitable high aspect ratio dielectric feature etch process window thatmeets the above challenges includes high magnetic field of up to about100 G, high RF power of up to about 2000 W and high inert gas flow ofbetween about 500 sccm and about 1000 sccm. Increased magnetic fieldprovides increased selectivity to the photomask material in the masklayer and reduces the likelihood of sidewall bowing. Increased inert gasflow provides a wider range of reactive gas dilution thereby decreasingresidence time and reactive species formation which in turn furtherimprove photoresist selectivity. In addition, the increased pump speedsof the present invention described above with regard to self alignedcontact etching may also be employed in high aspect ratio etching tofurther improve control of residence time and reactive species aformation.

The suitable high aspect ratio dielectric etch process comprises afluorocarbon gas, and oxygen comprising gas and an inert gas where thetotal gas flow is more than about 700 sccm an and the inert gascomprises more than about 90 percent of the total gas flow. A suitablehigh aspect ratio dielectric etch process has a reactive gas ratio offrom about 10:1 to about 15:1. In a specific embodiment, the ratio ofthe flow rate of the fluorocarbon gas to the flow rate of the oxygencomprising gas is about 1.5:1. In a specific embodiment the gascomposition used for etching comprises a fluorocarbon gas flow thatprovides from about 3 percent to about 6 percent of the total gas flow,an oxygen comprising gas comprising from about one percent to about fourpercent of the total gas flow and an inert gas making up more than 90percent of the total gas composition flow.

In the specific embodiment, the chamber pressure is maintained fromabout 20 mT to about 60 mT, the RF power is from about 1,000 watts toabout 2,000 watts, the magnetic field is maintained at about 100 G, andthe etch chamber is exhausted at a rate from about 48 chamber volumes toabout 80 chamber volumes per second. In another preferred embodiment,the substrate support is maintained at about −20 degrees C. while a wallor preferably, direct temperature control liner, is maintained at about15 C. In a specific preferred embodiment, the fluorocarbon gas is C₄F₆,the oxygen comprising gas is O₂ and the inert gas is argon.

FIGS. 35A and 35B illustrate, respectively, representative pre- andpost-metal via etch structures 3500 and 3505. Generally, metal via etchprocesses are important in forming interconnect structures between metallayers in an electronic device. Typically, the via formed in thedielectric material during a metal via etch is later filled by a metalsuch as, for example, a tungsten plug commonly used in aluminum basedmetalization schemes. Suitable metal via etch processes are selective tothe barrier layer 3515 or alternatively, selective to the underlyingmetal layer 3510.

FIG. 35A represents pre-etch metal via fill structure 3500 formed overmetal layer 3510. A barrier layer 3515, such as for example, a layercomprising titanium and titanium nitride, is formed over metal layer3510 and separates dielectric layer 3520 from metal layer 3510. Thedielectric layer 3520 is typically a TEOS based silicon dioxide and may,alternatively, be an HDP-CVD silicon dioxide film as well. FIG. 35A alsoillustrates the use of an anti-reflective coating layer 3525 undermasking layer 3530.

The specific dimensions of metal via etch structures 3500 and 3505 suchas the thickness of dielectric layer 3520 and the width of contact via3535 vary depending upon the type of via structure and upon the designrules used in a particular device. For example, the 0.25 micron featuredevice may have a dielectric layer 3520 about 10,000 angstroms thick andformed from TEOS with a barrier layer 3515 about 500 angstroms thick andformed from titanium nitride. Etch reactors having embodiments of thepresent invention are capable of etching contact vias having criticaldimensions of from about 0.25 microns to about 0.1 microns and viashaving aspect ratios of up to about 5:1.

A suitable metal via etch gas composition chemistry comprises afluorocarbon gas, and an oxygen comprising gas and an inert gas whereinthe total gas flow is less than about 500 sccm. In a particularembodiment, the inert gas flow rate provides about 85 percent of thetotal gas composition flow and the ratio of the inert gas to thereactive gases (i.e., the ratio of the inert gas flow rate to thecombined flow rates of the fluorocarbon gas and the oxygen comprisinggas) is between about 4:1 to about 6:1. In a specific preferredembodiment, the fluorocarbon gas provides about 9.5 percent of the totalgas composition flow, the chamber is maintained at about 20 mT, the RFpower is about 1500 watts, the magnetic field is about 50 Gauss and thesubstrate support and a wall, or preferably a temperature control lineradjacent the substrate support, are maintained at about the sametemperature.

In an alternative embodiment, the gas composition for a metal via etchprocess comprises a first fluorocarbon gas having a carbon to fluorineratio of 1:3, a second fluorocarbon gas having a carbon to fluorineratio of about 2:1 and any inert gas wherein the total gas flow of thegas composition is from about 200 sccm and to about 300 sccm. In aspecific preferred embodiment, the first fluorocarbon gas comprises fromabout 14 percent to about 18 percent of the total gas composition flow,and the second fluorocarbon gas comprises from about 13 percent to about16 percent of the total flow of the gas composition. In a specificpreferred embodiment, the ratio of the first fluorocarbon gas flow rateto the inert gas flow rate and the ratio of the second fluorocarbon gasflow rate to the inert gas flow rate is from about 0.2 to about 0.25. Inanother specific embodiment, the first fluorocarbon gas is C₂F₆, thesecond fluorocarbon gas is C₄F₈, the inert gas is argon, the chamber ismaintained at below about 200 mT, the RF power is about 1800 watts, themagnetic field is about 30 G and the chamber is exhausted at from about1,600 liters per second to about 2,000 liters per second.

FIGS. 36A and 36B illustrate feature structures representative of a maskopen application. FIGS. 36A and 36B are not drawn to scale. Some maskmaterials, such as for example, silicon nitride, are considerably moredifficult to etch than other mask materials and are referred to as “hardmasks.” FIG. 36A illustrates pre-hard mask etch structure 3600. Whilehard masked layer 3615 may be formed over a wide variety of other layersand materials, FIGS. 36A and 36B illustrate a hard mask layer 3615deposited directly on a silicon substrate 3610 formed from a suitablehard mask material, such as for example, silicon nitride. Nitride hardmasks comprise, for example, active area hard mask etching and deedconductor hard mask etching. FIG. 36A also illustrates the use of anantireflective coating layer 3620 below photomask pattern layer 3625.FIG. 36B illustrates post hard mask etch structure 3605 where thepattern of photomask layer 3625 has been transferred into hard masklayer 3615 by a suitable hard mask etch process performed in and etchprocessing chamber having embodiments of the present invention.

The suitable hard mask open process chemistry comprises a gascomposition comprising a hydrofluorocarbon gas, a fluorocarbon gas andan oxygen comprising gas wherein the total gas flow of the gascomposition is from about 50 sccm to about 200 sccm. In a specificembodiment, the hydrofluorocarbon gas comprises more than about half ofthe total gas composition flow rate and the oxygen comprising gas flowrate comprises less than about 15 percent of the total gas compositionflow rate. In another specific embodiment, the ratio of the flow rate ofthe hydrofluorocarbon gas to the flow rate of the fluorocarbon gas isabout 1.5:1. In another specific embodiment, the ratio of the combinedhydrofluorocarbon gas flow rate and the fluorocarbon gas flow rate tothe flow rate of the oxygen comprising gas is about 5.5:1.

In a specific preferred embodiment, the hydrofluorocarbon gas is a CHF₃,the fluorocarbon gas is a CF₄, the oxygen comprising gas is O₂, thepressure in the process chamber is maintained from about 20 mT to about80 mT and the RF power is about 500 watts. In yet another specificembodiment, the substrate support is maintained about 15 degrees Celsiushigher than a temperature of an adjacent wall, or preferably, atemperature controlled liner.

FIGS. 37A and 37B illustrate, respectively, pre-etch spacer structure3700 and post etch spacer structure 3705. FIGS. 37A and 37B are notillustrated to scale. Pre-etch spacer structure 3700 illustrates afeature 3715 formed over an underlayer 3720 on top of a siliconsubstrate 3710. A dielectric layer 3725 is formed over both the feature3715 and the underlayer 3720. Post etch spacer structure 3705 of FIG.37B is formed after conducting a suitable spacer etch process asdescribed in greater detail below. In post spacer etch structure 3705,spacer feature 3725 is formed by etching dielectric layer 3725 to exposethe top portion of the feature 3715 and remove most of the underlayer3720. In a representative spacer structure, feature 3715 could be formedfrom polysilicon and the underlayer 3720 could be formed from silicondioxide.

In general, spacer etch processes may be divided into two categoriesbased upon selectivity to the underlayer 3720. For example, in theillustrated spacer structure described above, the spacer etch process isselective to an underlying silicon dioxide layer. Alternatively, whenremoval of both dielectric layer 3725 an underlying layer 3720 isdesired, a spacer etch process selective to the silicon substrate 3710may be used in order to etch both dielectric layer 3725 and underlyinglayer 3720 before stopping upon reaching silicon substrate 3710.

The gas composition used to form a suitable spacer etch processchemistry comprises a hydrofluorocarbon gas, a fluorocarbon gas, anoxygen comprising gas and an inert gas with a total gas flow of the gascomposition is from about 50 sccm to about 200 sccm. In a specificembodiment, the hydrofluorocarbon gas flow comprises more than about 40percent of the total gas flow and the oxygen comprising gas comprisesless than about 5 percent of the total gas composition flow rate. Inanother specific embodiment, the ratio of the hydrofluorocarbon gas flowto the fluorocarbon gas flow is about 2.5:1. In yet another specificembodiment, the combined flow rate of the hydrofluorocarbon gas and thefluorocarbon gas to the flow rate of the inert gas is about 1.75:1.

In a specific preferred embodiment, the fluorocarbon gas is CF₄, thehydrofluorocarbon gas is CHF₃, the oxygen comprising gas is O₂, theinert gas is argon, the pressure of the etch chamber is maintained atbetween about 20 mT to about 80 mT, the RF power is about 400 watts, thesubstrate support is maintained at a temperature about 25 degreesCelsius higher than an adjacent wall, or preferably, an adjacent directtemperature controlled liner.

FIGS. 38A and 38B illustrate representative structures for etching dualdamascene features. FIG. 38A illustrates pre-dual damascene dielectricetch structure 3800 and FIG. 38B illustrates post dual damascenedielectric etch structure 3805. FIGS. 38A and B are not illustrated toscale.

FIG. 38A illustrates a basic dual damascene structure formed over inmetal layer, such as for example, a copper layer 3810. Two dielectriclayers, namely trench dielectric layer 3830 and via dielectric layer3820, are etched during a suitable dual damascene dielectric etchprocess, such as those discussed in more detail below. A bottom nitridelayer 3815 separates the copper layer 3810 from the via dielectric layer3820. Intermediate nitride layer 3825 separates the trench dielectriclayer 3830 from the via dielectric layer 3820. In some dual damasceneetch processes, the intermediate nitride layer 3825 is used as a stoplayer for etching the trench dielectric layer 3830 and the bottomnitride layer 3815 is used as a stop layer for etching the viadielectric layer 3820. FIG. 38B illustrates post dual damascene etchstructure 3805 that includes a via feature 3850 and an interconnectfeature 3855. Typically, the via feature 3850 and the interconnectfeature 3855 are filled by subsequent metalization processes.

There are at least three fundamental process flows used to form dualdamascene features: self aligned, trench first, and via first. Whileother structures may be and are used, in general, typical dual damasceneetch processes begin with a pre-etch structure, such as structure 3800of FIG. 38A, and finish with a structure having a via feature 3850 andan interconnect feature 3855 as illustrated in FIG. 38B.

In a self aligned dual damascene process, a via pattern is etched firstby opening intermediate nitride layer 3825. During a subsequent etchstep that uses bottom nitride layer 3815 as an etch stop layer, both thevia feature 3850 and the interconnect feature 3855 are formed. Finally,the bottom nitride layer 3815 is removed to expose copper layer 3810.

In a trench first dual damascene process, the mask pattern layer 3835forms the pattern for the interconnect feature 3855 and the upperportion 3860 of the via feature 3850. The resulting intermediatestructure comprises interconnect 3855 and the upper portion of viafeature 3860. This intermediate structure is then patterned and etchedto form the lower portion of via feature 3865 using bottom nitride layerof 3815 as an etch stop layer. A subsequent etch step is then used toremove bottom nitride layer 3815 and expose the copper layer 3810.

In a via first dual damascene process, a via pattern is formed by themask pattern layer 3835. The via pattern is subsequently transferred toboth of the dielectric layers 3830 and 3820 and to the intermediatenitride layer 3825. This step forms an intermediate structure comprisingthe lower portion 3865 of via structure 3850. Next, a trench maskpattern is formed over this intermediate structure to pattern thetrenches, namely the interconnect feature 3855 and the upper portion ofcontact feature 3860. The bottom nitride layer 3815 is subsequentlyremoved exposing the copper layer 3810.

The exact dimensions of the dual damascene structures 3800 and 3805 willvary depending upon a number of considerations, such as for example, thetype of dual damascene process sequence and the design rules of aparticular device. The particular design rules determine the dimensionsfor trench feature 3855, via feature 3850 and, more importantly, thecritical dimension of contact region 3865. Etch process chambers havingembodiments of the present invention are capable of etching dualdamascene structures having critical dimensions of about 0.3 microns toabout 0.25 microns and even structures having critical dimensions ofabout 0.1 microns to about 0.2 microns.

A suitable dual damascene trench etch process chemistry comprises afluorocarbon gas having a carbon to fluorine ratio of about 1:3 and agas comprising carbon and oxygen. In a preferred embodiment, most of thegas composition comprises a gas comprising carbon and oxygen with thetotal flow of the gas composition being from between about 200 sccm toabout 400 sccm. In a specific preferred embodiment, at least about 60percent of the gas composition comprises a gas comprising oxygen andcarbon. In another specific embodiment, the ratio of the flow rate ofthe gas comprising oxygen and carbon to the flow rate of thefluorocarbon gas is about 1.67:1. In yet another specific preferredembodiment, the fluorocarbon gas is C₂F₆, the gas comprising oxygen andcarbon is CO, the pressure to processing chamber is maintained atbetween about 100 mT to about 200 mT, the magnetic field in theprocessing region is about 30 G and the RF power is about 1500 watts.

In an alternative embodiment where the dual damascene structurecomprises a nitride stop layer, a suitable dual damascene etch processchemistry comprises a gas composition comprising a polymerizingfluorocarbon having a C:F ratio of about 1:2, and oxygen comprising gasand an inert gas. In a specific preferred embodiment, the inert gascomprises more than about 90 percent of the total gas composition flow,and the oxygen comprising gas comprises less than about 1 percent of thetotal gas composition flow. In another specific preferred embodiment,the ratio of the inert gas flow to the combined flow rates of thepolymerizing fluorocarbon gas and the oxygen comprising gas is fromabout 20:1 to about 22:1. In a specific preferred embodiment thepolymerizing fluorocarbon gas is C₄F₈ and the oxygen comprising gas isO₂ and the ratio of the C₄F₈ flow rate to the O₂ flow rate is about 3:1about 4:1. In a specific preferred embodiment, the gas compositioncomprises a C₄F₈, O₂ and Ar wherein the Ar flow rate is more than about95 percent of the total gas composition flow rate, the C₄F₈ flow ratecomprises more than about three percent of the total gas compositionflow rate, the chamber is maintained at about 80 mT, the RF power levelis about 1800 watts, the magnetic field in a processing region is about20 G, the substrate support is maintained at about 10 degrees Celsiushigher than the temperature of an adjacent wall or, preferably, atemperature controlled liner.

One suitable dual damascene via etch chemistry comprises a gascomposition comprising a fluorocarbon gas having a C:F ratio of about2:3, and oxygen comprising gas and an inert gas. In a specific preferredembodiment, the etch chamber is maintained between about 30 mT to about80 mT, the total gas composition flow rate is from about 300 sccm toabout 500 sccm an and the ratio of the inert gas flow rate to thecombined flow rates of the fluorocarbon gas having a C:F ratio of about2:3 and an oxygen comprising gas is from about 5:1 to about 7:1 and morepreferably, about 6:1. In a specific preferred embodiment, thefluorocarbon gas having a C:F ratio of about 2:3 is C₄F₆, the oxygencomprising gas is O₂ and inert gas is argon, the C₄F₆ comprises about 5%to about 9% of the total gas composition flow and the inert gas flowcomprises more than about 80 percent of the gas composition flow, thechamber is maintained at about 50 mT, the RF power is about 1800 wattsand a magnetic field in the processing region is about 50 G.

In another alternative embodiment, a two-step dual damascene via etchprocess may be used. A suitable to two-step dual damascene via etchprocess chemistry comprises a gas composition comprising a polymerizingfluorocarbon gas, a hydrofluorocarbon gas, an oxygen comprising gas andan inert gas wherein the ratio of the inert gas flow to the combined gasflows of the polymerizing fluorocarbon gas, the hydrofluorocarbon gasand the oxygen comprising gas is from about 4:1 to about 6:1; and thepolymerizing fluorocarbon gas used in the second step is greater thanthe first step. In a specific preferred embodiment of a suitabletwo-step dual damascene via process, the first step gas compositioncomprises less than about three percent polymerizing fluorocarbon gas,about 4 percent to about 5 percent oxygen comprising gas, about 7percent to about nine percent hydrofluorocarbon gas and more than about80 percent inert gas while the second step comprises more than about 4percent polymerizing fluorocarbon gas, about 4 percent to about 5percent oxygen comprising gas, about 7 percent to about 8 percenthydrofluorocarbon gas and more than about 80 percent inert gas. In aspecific preferred embodiment, the total gas composition flow rate ineach etch step is from about 500 sccm to about 1,000 sccm, the pressureis about 50 mT, the RF power level is about 2,000 watts and the magneticfield apply to the processing region is about 15 G. In another specificpreferred embodiment, the polymerizing fluorocarbon gas is C₄F₆, thehydrofluorocarbon gas is CHF₃, the oxygen comprising gas is O₂ and theinert gas is Ar.

It is to be appreciated that each of the alternative etch processchamber embodiments and critical etch processes described above mayincorporate aspects of the high exhaust pump rate and reduced reactivespecies residence time control feature of the present invention.

The terms “below”, “above”, “bottom”, “top”, “up”, “down”, “first”, and“second” and other positional terms are shown with respect to theembodiments in the figures and may be varied depending on the relativeorientation of the processing system.

Furthermore, in this specification, including particularly the claims,the use of “comprising” with “a” or “the”, and variations thereof meansthat the item(s) or list(s) referenced includes at least the enumerateditem(s) or list(s) and furthermore may include a plurality of theenumerated item(s) or list(s), unless otherwise stated.

Although the embodiment of the invention which incorporate the teachingsof the present invention which has been shown and described in detailherein, those skilled in the art can readily devise other variedembodiments which still incorporate the teachings and do not depart fromthe spirit of the invention.

What is claimed is:
 1. A method of plasma etching features on adielectric layer on a substrate disposed in a magnetically enhancedthermally controlled plasma etch chamber, comprising: (a) disposing asubstrate in a processing region of a thermally controlled plasma etchchamber; (b) controlling the temperature of a wall disposed adjacent tothe processing region of the thermally controlled plasma etch chamber tocreate a low temperature that is conducive to adhesion of polymerby-product on said wall; (c) controlling the temperature of a substratesupport; (d) maintaining a pressure in the processing region; (e)flowing a gas composition through a nozzle and into the processingregion, said nozzle being at a temperature that is higher than said wallto prevent to adhesion of polymer by-product on said nozzle; (f)coupling RF energy into the processing region to form a plasma from thegas composition; and (g) providing a magnetic field in the processingregion and transverse to the substrate.
 2. A method of plasma etchingfeatures on a dielectric layer according to claim 1 wherein step (d)comprises evacuating the processing region at between about 1400 toabout 1800 liters per minute.
 3. A method of plasma etching features ona dielectric layer according to claim 1 wherein the step (c) isperformed by circulating a fluid in a channel formed within a linerdisposed adjacent to the processing region.
 4. A method of plasmaetching features on a dielectric layer according to claim 1 wherein step(f) comprises capacitively coupling RF energy.
 5. A method of plasmaetching features on a dielectric layer according to claim 1 wherein step(g) comprises rotating the magnetic field.
 6. A method of plasma etchingfeatures on a dielectric layer according to claims 1, further comprisingforming a magnetic field transverse to a pumping annulus of themagnetically enhanced thermally controlled plasma etch chamber.
 7. Amethod of plasma etching features on a dielectric layer according toclaim 1 wherein the gas composition comprises a fluorocarbon, an oxygencomprising gas and an inert gas wherein the total flow of the gascomposition is between about 400 sccm to about 800 sccm.
 8. A method ofplasma etching features on a dielectric layer according to claim 1,further comprising evacuating the chamber at a rate providing aresidence time of less than about 70 ms in said chamber.
 9. A method ofplasma etching features on a dielectric layer according to claim 1wherein the gas composition comprises a fluorocarbon gas having a C:Fratio of 1:3, and a gas comprising carbon and oxygen wherein the totalflow of the gas composition between about 200 sccm to about 400 sccm.10. A method of plasma etching features on a dielectric layer accordingto claims 9 wherein the fluorocarbon gas is C₂F₆, the gas comprisingcarbon and oxygen is CO and the feature is a dual damascene trench. 11.A method of plasma etching features on a dielectric layer according toclaim 1, wherein the gas composition comprises a hydrofluorocarbon gas,a fluorocarbon gas, and an oxygen comprising gas wherein the total flowof the gas composition is between about 50 sccm to about 200 sccm.
 12. Amethod of plasma etching features on a dielectric layer according toclaim 11, wherein the hydrofluorocarbon is CHF₃, the fluorocarbon gas isCF₄, and the oxygen comprising gas is O₂.
 13. A method of plasma etchingfeatures on a dielectric layer according to claim 1 wherein the gascomposition comprises a hydrofluorocarbon gas, a fluorocarbon gas, anoxygen comprising gas and an inert gas wherein the total flow of the gascomposition between about 50 sccm to about 200 sccm.
 14. A method ofplasma etching features on a dielectric layer according to claim 13wherein the fluorocarbon gas is CF₄, the hydrofluorocarbon gas is CHF₃,the oxygen comprising gas is O₂, the inert gas is argon, the pressure inthe processing chamber is between about 20 mT to about 80 mT.
 15. Amethod of plasma etching features on a dielectric layer according toclaim 1, wherein the gas composition comprises a first fluorocarbonhaving a C:F ratio of 1:3, a second fluorocarbon having a C:F ratio of2:1, and an inert gas, and wherein the total flow of the gas compositionis between about 200 sccm to about 300 sccm.
 16. A method of plasmaetching features on a dielectric layer according to claim 15, whereinthe first fluorocarbon gas comprises about 14 to about 18 percent of thetotal flow of the gas composition, the second fluorocarbon gas comprisesbetween about 13 to about 16 percent of the total flow of the gascomposition and the inert gas comprises more than 65 percent of the gascomposition.
 17. A method of plasma etching features on a dielectriclayer according to claims 16, wherein the first fluorocarbon gas isC₂F₆, the second fluorocarbon gas is C₄F₈.
 18. A method of plasmaetching features on a dielectric layer according to claim 1 wherein thegas composition comprises a fluorocarbon, an oxygen comprising gas andan inert gas wherein the total flow of the gas composition between about300 sccm to about 500 sccm.
 19. A method of plasma etching features on adielectric layer according to claim, 18 wherein the fluorocarbon gas isC₄F₆, and the oxygen comprising gas is O₂.
 20. A method of plasmaetching features on a dielectric layer according to claim 18, whereinthe pressure in the processing chamber is between about 20 mT to about60 mT, and further comprises maintaining a 35° C. temperature differencebetween the wall temperature and the substrate support temperature. 21.A method of plasma etching features on a dielectric layer according toclaim 18, wherein the fluorocarbon comprises about 3 to about 5 percentof the total flow of the gas composition, the oxygen comprising gascomprises between about 1 to about 4 percent of the total flow of thegas composition and the inert gas comprises more than 90 percent of thegas composition.
 22. A method of plasma etching features on a dielectriclayer according to claims 21, wherein the fluorocarbon gas is C₄F₆, andthe oxygen comprising gas is O₂.
 23. A method of plasma etching featureson a dielectric layer according to claim 18, wherein the ratio of thefluorocarbon gas flow to the inert gas flow is about 0.5 and the ratioof the oxygen comprising gas flow to the inert gas flow is about 0.03.24. A method of plasma etching features on a dielectric layer accordingto claim 23 wherein the fluorocarbon comprises about 7 to about 10percent of the total flow of the gas composition, the oxygen comprisinggas comprises between about 4 to about 6 percent of the total flow ofthe gas composition and the inert gas comprises more than 80 percent ofthe gas composition, and wherein said fluorocarbon compriseshexafluoro-1,3-butadiene.